root/chrome/browser/sync/glue/bookmark_change_processor.cc

DEFINITIONS

1. model_associator_
2. StartImpl
3. UpdateSyncNodeProperties
4. EncodeFavicon
5. RemoveOneSyncNode
6. RemoveSyncNodeHierarchy
7. RemoveAllSyncNodes
8. RemoveAllChildNodes
9. BookmarkModelLoaded
10. BookmarkModelBeingDeleted
11. BookmarkNodeAdded
12. CreateSyncNode
13. BookmarkNodeRemoved
14. BookmarkAllNodesRemoved
15. BookmarkNodeChanged
16. BookmarkMetaInfoChanged
17. BookmarkNodeMoved
18. BookmarkNodeFaviconChanged
19. BookmarkNodeChildrenReordered
20. PlaceSyncNode
21. ApplyChangesFromSyncModel
22. UpdateBookmarkWithSyncData
23. UpdateTransactionVersion
24. CreateBookmarkNode
25. SetBookmarkFavicon
26. SetBookmarkMetaInfo
27. SetSyncNodeMetaInfo
28. ApplyBookmarkFavicon
29. SetSyncNodeFavicon

// Copyright 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "chrome/browser/sync/glue/bookmark_change_processor.h"

#include <map>
#include <stack>
#include <vector>

#include "base/location.h"
#include "base/strings/string16.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "chrome/browser/bookmarks/bookmark_model.h"
#include "chrome/browser/bookmarks/bookmark_model_factory.h"
#include "chrome/browser/bookmarks/bookmark_utils.h"
#include "chrome/browser/favicon/favicon_service.h"
#include "chrome/browser/favicon/favicon_service_factory.h"
#include "chrome/browser/history/history_service.h"
#include "chrome/browser/history/history_service_factory.h"
#include "chrome/browser/profiles/profile.h"
#include "chrome/browser/sync/profile_sync_service.h"
#include "chrome/browser/undo/bookmark_undo_service.h"
#include "chrome/browser/undo/bookmark_undo_service_factory.h"
#include "chrome/browser/undo/bookmark_undo_utils.h"
#include "content/public/browser/browser_thread.h"
#include "sync/internal_api/public/change_record.h"
#include "sync/internal_api/public/read_node.h"
#include "sync/internal_api/public/write_node.h"
#include "sync/internal_api/public/write_transaction.h"
#include "sync/syncable/entry.h"  // TODO(tim): Investigating bug 121587.
#include "sync/syncable/syncable_write_transaction.h"
#include "ui/gfx/favicon_size.h"
#include "ui/gfx/image/image_util.h"

using content::BrowserThread;
using syncer::ChangeRecord;
using syncer::ChangeRecordList;

namespace browser_sync {

static const char kMobileBookmarksTag[] = "synced_bookmarks";

BookmarkChangeProcessor::BookmarkChangeProcessor(
    BookmarkModelAssociator* model_associator,
    DataTypeErrorHandler* error_handler)
    : ChangeProcessor(error_handler),
      bookmark_model_(NULL),
      model_associator_(model_associator) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  DCHECK(model_associator);
  DCHECK(error_handler);
}

BookmarkChangeProcessor::~BookmarkChangeProcessor() {
  if (bookmark_model_)
    bookmark_model_->RemoveObserver(this);
}

void BookmarkChangeProcessor::StartImpl(Profile* profile) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  DCHECK(profile);
  profile_ = profile;
  DCHECK(!bookmark_model_);
  bookmark_model_ = BookmarkModelFactory::GetForProfile(profile);
  DCHECK(bookmark_model_->loaded());
  bookmark_model_->AddObserver(this);
}

void BookmarkChangeProcessor::UpdateSyncNodeProperties(
    const BookmarkNode* src,
    BookmarkModel* model,
    syncer::WriteNode* dst) {
  // Set the properties of the item.
  dst->SetIsFolder(src->is_folder());
  dst->SetTitle(base::UTF16ToWideHack(src->GetTitle()));
  sync_pb::BookmarkSpecifics bookmark_specifics(dst->GetBookmarkSpecifics());
  if (!src->is_folder())
    bookmark_specifics.set_url(src->url().spec());
  bookmark_specifics.set_creation_time_us(src->date_added().ToInternalValue());
  dst->SetBookmarkSpecifics(bookmark_specifics);
  SetSyncNodeFavicon(src, model, dst);
  SetSyncNodeMetaInfo(src, dst);
}

// static
void BookmarkChangeProcessor::EncodeFavicon(
    const BookmarkNode* src,
    BookmarkModel* model,
    scoped_refptr<base::RefCountedMemory>* dst) {
  const gfx::Image& favicon = model->GetFavicon(src);

  // Check for empty images.  This can happen if the favicon is
  // still being loaded.
  if (favicon.IsEmpty())
    return;

  // Re-encode the BookmarkNode's favicon as a PNG, and pass the data to the
  // sync subsystem.
  *dst = favicon.As1xPNGBytes();
}

void BookmarkChangeProcessor::RemoveOneSyncNode(syncer::WriteNode* sync_node) {
  // This node should have no children.
  DCHECK(!sync_node->HasChildren());
  // Remove association and delete the sync node.
  model_associator_->Disassociate(sync_node->GetId());
  sync_node->Tombstone();
}

void BookmarkChangeProcessor::RemoveSyncNodeHierarchy(
    const BookmarkNode* topmost) {
  int64 new_version =
      syncer::syncable::kInvalidTransactionVersion;
  {
    syncer::WriteTransaction trans(FROM_HERE, share_handle(), &new_version);
    syncer::WriteNode topmost_sync_node(&trans);
    if (!model_associator_->InitSyncNodeFromChromeId(topmost->id(),
                                                     &topmost_sync_node)) {
      error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
                                                          std::string());
      return;
    }
    // Check that |topmost| has been unlinked.
    DCHECK(topmost->is_root());
    RemoveAllChildNodes(&trans, topmost->id());
    // Remove the node itself.
    RemoveOneSyncNode(&topmost_sync_node);
  }

  // Don't need to update versions of deleted nodes.
  UpdateTransactionVersion(new_version, bookmark_model_,
                           std::vector<const BookmarkNode*>());
}

void BookmarkChangeProcessor::RemoveAllSyncNodes() {
  int64 new_version = syncer::syncable::kInvalidTransactionVersion;
  {
    syncer::WriteTransaction trans(FROM_HERE, share_handle(), &new_version);

    RemoveAllChildNodes(&trans, bookmark_model_->bookmark_bar_node()->id());
    RemoveAllChildNodes(&trans, bookmark_model_->other_node()->id());
    // Remove mobile bookmarks node only if it is present.
    const int64 mobile_bookmark_id = bookmark_model_->mobile_node()->id();
    if (model_associator_->GetSyncIdFromChromeId(mobile_bookmark_id) !=
            syncer::kInvalidId) {
      RemoveAllChildNodes(&trans, bookmark_model_->mobile_node()->id());
    }
  }

  // Don't need to update versions of deleted nodes.
  UpdateTransactionVersion(new_version, bookmark_model_,
                           std::vector<const BookmarkNode*>());
}

void BookmarkChangeProcessor::RemoveAllChildNodes(
    syncer::WriteTransaction* trans, const int64& topmost_node_id) {
  syncer::WriteNode topmost_node(trans);
  if (!model_associator_->InitSyncNodeFromChromeId(topmost_node_id,
                                                   &topmost_node)) {
    error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
                                                        std::string());
    return;
  }
  const int64 topmost_sync_id = topmost_node.GetId();

  // Do a DFS and delete all the child sync nodes, use sync id instead of
  // bookmark node ids since the bookmark nodes may already be deleted.
  // The equivalent recursive version of this iterative DFS:
  // remove_all_children(node_id, topmost_node_id):
  //    node.initByIdLookup(node_id)
  //    while(node.GetFirstChildId() != syncer::kInvalidId)
  //      remove_all_children(node.GetFirstChildId(), topmost_node_id)
  //    if(node_id != topmost_node_id)
  //      delete node

  std::stack<int64> dfs_sync_id_stack;
  // Push the topmost node.
  dfs_sync_id_stack.push(topmost_sync_id);
  while (!dfs_sync_id_stack.empty()) {
    const int64 sync_node_id = dfs_sync_id_stack.top();
    syncer::WriteNode node(trans);
    node.InitByIdLookup(sync_node_id);
    if (!node.GetIsFolder() || node.GetFirstChildId() == syncer::kInvalidId) {
      // All children of the node has been processed, delete the node and
      // pop it off the stack.
      dfs_sync_id_stack.pop();
      // Do not delete the topmost node.
      if (sync_node_id != topmost_sync_id) {
        RemoveOneSyncNode(&node);
      } else {
        // if we are processing topmost node, all other nodes must be processed
        // the stack should be empty.
        DCHECK(dfs_sync_id_stack.empty());
      }
    } else {
      int64 child_id = node.GetFirstChildId();
      if (child_id != syncer::kInvalidId) {
        dfs_sync_id_stack.push(child_id);
      }
    }
  }
}

void BookmarkChangeProcessor::BookmarkModelLoaded(BookmarkModel* model,
                                                  bool ids_reassigned) {
  NOTREACHED();
}

void BookmarkChangeProcessor::BookmarkModelBeingDeleted(
    BookmarkModel* model) {
  NOTREACHED();
  bookmark_model_ = NULL;
}

void BookmarkChangeProcessor::BookmarkNodeAdded(BookmarkModel* model,
                                                const BookmarkNode* parent,
                                                int index) {
  DCHECK(share_handle());

  int64 new_version = syncer::syncable::kInvalidTransactionVersion;
  int64 sync_id = syncer::kInvalidId;
  {
    // Acquire a scoped write lock via a transaction.
    syncer::WriteTransaction trans(FROM_HERE, share_handle(), &new_version);
    sync_id = CreateSyncNode(parent, model, index, &trans,
                             model_associator_, error_handler());
  }

  if (syncer::kInvalidId != sync_id) {
    // Siblings of added node in sync DB will also be updated to reflect new
    // PREV_ID/NEXT_ID and thus get a new version. But we only update version
    // of added node here. After switching to ordinals for positioning,
    // PREV_ID/NEXT_ID will be deprecated and siblings will not be updated.
    UpdateTransactionVersion(
        new_version, model,
        std::vector<const BookmarkNode*>(1, parent->GetChild(index)));
  }
}

// static
int64 BookmarkChangeProcessor::CreateSyncNode(const BookmarkNode* parent,
    BookmarkModel* model, int index, syncer::WriteTransaction* trans,
    BookmarkModelAssociator* associator,
    DataTypeErrorHandler* error_handler) {
  const BookmarkNode* child = parent->GetChild(index);
  DCHECK(child);

  // Create a WriteNode container to hold the new node.
  syncer::WriteNode sync_child(trans);

  // Actually create the node with the appropriate initial position.
  if (!PlaceSyncNode(CREATE, parent, index, trans, &sync_child, associator)) {
    error_handler->OnSingleDatatypeUnrecoverableError(FROM_HERE,
        "Sync node creation failed; recovery unlikely");
    return syncer::kInvalidId;
  }

  UpdateSyncNodeProperties(child, model, &sync_child);

  // Associate the ID from the sync domain with the bookmark node, so that we
  // can refer back to this item later.
  associator->Associate(child, sync_child.GetId());

  return sync_child.GetId();
}

void BookmarkChangeProcessor::BookmarkNodeRemoved(BookmarkModel* model,
                                                  const BookmarkNode* parent,
                                                  int index,
                                                  const BookmarkNode* node) {
  RemoveSyncNodeHierarchy(node);
}

void BookmarkChangeProcessor::BookmarkAllNodesRemoved(BookmarkModel* model) {
  RemoveAllSyncNodes();
}

void BookmarkChangeProcessor::BookmarkNodeChanged(BookmarkModel* model,
                                                  const BookmarkNode* node) {
  // We shouldn't see changes to the top-level nodes.
  if (model->is_permanent_node(node)) {
    NOTREACHED() << "Saw update to permanent node!";
    return;
  }

  int64 new_version = syncer::syncable::kInvalidTransactionVersion;
  {
    // Acquire a scoped write lock via a transaction.
    syncer::WriteTransaction trans(FROM_HERE, share_handle(), &new_version);

    // Lookup the sync node that's associated with |node|.
    syncer::WriteNode sync_node(&trans);
    if (!model_associator_->InitSyncNodeFromChromeId(node->id(), &sync_node)) {
      // TODO(tim): Investigating bug 121587.
      if (model_associator_->GetSyncIdFromChromeId(node->id()) ==
                                                   syncer::kInvalidId) {
        error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
            "Bookmark id not found in model associator on BookmarkNodeChanged");
        LOG(ERROR) << "Bad id.";
      } else if (!sync_node.GetEntry()->good()) {
        error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
            "Could not InitByIdLookup on BookmarkNodeChanged, good() failed");
        LOG(ERROR) << "Bad entry.";
      } else if (sync_node.GetEntry()->GetIsDel()) {
        error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
            "Could not InitByIdLookup on BookmarkNodeChanged, is_del true");
        LOG(ERROR) << "Deleted entry.";
      } else {
        syncer::Cryptographer* crypto = trans.GetCryptographer();
        syncer::ModelTypeSet encrypted_types(trans.GetEncryptedTypes());
        const sync_pb::EntitySpecifics& specifics =
            sync_node.GetEntry()->GetSpecifics();
        CHECK(specifics.has_encrypted());
        const bool can_decrypt = crypto->CanDecrypt(specifics.encrypted());
        const bool agreement = encrypted_types.Has(syncer::BOOKMARKS);
        if (!agreement && !can_decrypt) {
          error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
              "Could not InitByIdLookup on BookmarkNodeChanged, "
              " Cryptographer thinks bookmarks not encrypted, and CanDecrypt"
              " failed.");
          LOG(ERROR) << "Case 1.";
        } else if (agreement && can_decrypt) {
          error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
              "Could not InitByIdLookup on BookmarkNodeChanged, "
              " Cryptographer thinks bookmarks are encrypted, and CanDecrypt"
              " succeeded (?!), but DecryptIfNecessary failed.");
          LOG(ERROR) << "Case 2.";
        } else if (agreement) {
          error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
              "Could not InitByIdLookup on BookmarkNodeChanged, "
              " Cryptographer thinks bookmarks are encrypted, but CanDecrypt"
              " failed.");
          LOG(ERROR) << "Case 3.";
        } else {
          error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
              "Could not InitByIdLookup on BookmarkNodeChanged, "
              " Cryptographer thinks bookmarks not encrypted, but CanDecrypt"
              " succeeded (super weird, btw)");
          LOG(ERROR) << "Case 4.";
        }
      }
      return;
    }

    UpdateSyncNodeProperties(node, model, &sync_node);

    DCHECK_EQ(sync_node.GetIsFolder(), node->is_folder());
    DCHECK_EQ(model_associator_->GetChromeNodeFromSyncId(
              sync_node.GetParentId()),
              node->parent());
    DCHECK_EQ(node->parent()->GetIndexOf(node), sync_node.GetPositionIndex());
  }

  UpdateTransactionVersion(new_version, model,
                           std::vector<const BookmarkNode*>(1, node));
}

void BookmarkChangeProcessor::BookmarkMetaInfoChanged(
    BookmarkModel* model, const BookmarkNode* node) {
  BookmarkNodeChanged(model, node);
}

void BookmarkChangeProcessor::BookmarkNodeMoved(BookmarkModel* model,
      const BookmarkNode* old_parent, int old_index,
      const BookmarkNode* new_parent, int new_index) {
  const BookmarkNode* child = new_parent->GetChild(new_index);
  // We shouldn't see changes to the top-level nodes.
  if (model->is_permanent_node(child)) {
    NOTREACHED() << "Saw update to permanent node!";
    return;
  }

  int64 new_version = syncer::syncable::kInvalidTransactionVersion;
  {
    // Acquire a scoped write lock via a transaction.
    syncer::WriteTransaction trans(FROM_HERE, share_handle(), &new_version);

    // Lookup the sync node that's associated with |child|.
    syncer::WriteNode sync_node(&trans);
    if (!model_associator_->InitSyncNodeFromChromeId(child->id(), &sync_node)) {
      error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
                                                          std::string());
      return;
    }

    if (!PlaceSyncNode(MOVE, new_parent, new_index, &trans, &sync_node,
                       model_associator_)) {
      error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
                                                          std::string());
      return;
    }
  }

  UpdateTransactionVersion(new_version, model,
                           std::vector<const BookmarkNode*>(1, child));
}

void BookmarkChangeProcessor::BookmarkNodeFaviconChanged(
    BookmarkModel* model,
    const BookmarkNode* node) {
  BookmarkNodeChanged(model, node);
}

void BookmarkChangeProcessor::BookmarkNodeChildrenReordered(
    BookmarkModel* model, const BookmarkNode* node) {
  int64 new_version = syncer::syncable::kInvalidTransactionVersion;
  std::vector<const BookmarkNode*> children;
  {
    // Acquire a scoped write lock via a transaction.
    syncer::WriteTransaction trans(FROM_HERE, share_handle(), &new_version);

    // The given node's children got reordered. We need to reorder all the
    // children of the corresponding sync node.
    for (int i = 0; i < node->child_count(); ++i) {
      const BookmarkNode* child = node->GetChild(i);
      children.push_back(child);

      syncer::WriteNode sync_child(&trans);
      if (!model_associator_->InitSyncNodeFromChromeId(child->id(),
                                                       &sync_child)) {
        error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
                                                            std::string());
        return;
      }
      DCHECK_EQ(sync_child.GetParentId(),
                model_associator_->GetSyncIdFromChromeId(node->id()));

      if (!PlaceSyncNode(MOVE, node, i, &trans, &sync_child,
                         model_associator_)) {
        error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
                                                            std::string());
        return;
      }
    }
  }

  // TODO(haitaol): Filter out children that didn't actually change.
  UpdateTransactionVersion(new_version, model, children);
}

// static
bool BookmarkChangeProcessor::PlaceSyncNode(MoveOrCreate operation,
      const BookmarkNode* parent, int index, syncer::WriteTransaction* trans,
      syncer::WriteNode* dst, BookmarkModelAssociator* associator) {
  syncer::ReadNode sync_parent(trans);
  if (!associator->InitSyncNodeFromChromeId(parent->id(), &sync_parent)) {
    LOG(WARNING) << "Parent lookup failed";
    return false;
  }

  bool success = false;
  if (index == 0) {
    // Insert into first position.
    success = (operation == CREATE) ?
        dst->InitBookmarkByCreation(sync_parent, NULL) :
        dst->SetPosition(sync_parent, NULL);
    if (success) {
      DCHECK_EQ(dst->GetParentId(), sync_parent.GetId());
      DCHECK_EQ(dst->GetId(), sync_parent.GetFirstChildId());
      DCHECK_EQ(dst->GetPredecessorId(), syncer::kInvalidId);
    }
  } else {
    // Find the bookmark model predecessor, and insert after it.
    const BookmarkNode* prev = parent->GetChild(index - 1);
    syncer::ReadNode sync_prev(trans);
    if (!associator->InitSyncNodeFromChromeId(prev->id(), &sync_prev)) {
      LOG(WARNING) << "Predecessor lookup failed";
      return false;
    }
    success = (operation == CREATE) ?
        dst->InitBookmarkByCreation(sync_parent, &sync_prev) :
        dst->SetPosition(sync_parent, &sync_prev);
    if (success) {
      DCHECK_EQ(dst->GetParentId(), sync_parent.GetId());
      DCHECK_EQ(dst->GetPredecessorId(), sync_prev.GetId());
      DCHECK_EQ(dst->GetId(), sync_prev.GetSuccessorId());
    }
  }
  return success;
}

// ApplyModelChanges is called by the sync backend after changes have been made
// to the sync engine's model.  Apply these changes to the browser bookmark
// model.
void BookmarkChangeProcessor::ApplyChangesFromSyncModel(
    const syncer::BaseTransaction* trans,
    int64 model_version,
    const syncer::ImmutableChangeRecordList& changes) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  // A note about ordering.  Sync backend is responsible for ordering the change
  // records in the following order:
  //
  // 1. Deletions, from leaves up to parents.
  // 2. Existing items with synced parents & predecessors.
  // 3. New items with synced parents & predecessors.
  // 4. Items with parents & predecessors in the list.
  // 5. Repeat #4 until all items are in the list.
  //
  // "Predecessor" here means the previous item within a given folder; an item
  // in the first position is always said to have a synced predecessor.
  // For the most part, applying these changes in the order given will yield
  // the correct result.  There is one exception, however: for items that are
  // moved away from a folder that is being deleted, we will process the delete
  // before the move.  Since deletions in the bookmark model propagate from
  // parent to child, we must move them to a temporary location.
  BookmarkModel* model = bookmark_model_;

  // We are going to make changes to the bookmarks model, but don't want to end
  // up in a feedback loop, so remove ourselves as an observer while applying
  // changes.
  model->RemoveObserver(this);

  // Changes made to the bookmark model due to sync should not be undoable.
#if !defined(OS_ANDROID)
  ScopedSuspendBookmarkUndo suspend_undo(profile_);
#endif

  // Notify UI intensive observers of BookmarkModel that we are about to make
  // potentially significant changes to it, so the updates may be batched. For
  // example, on Mac, the bookmarks bar displays animations when bookmark items
  // are added or deleted.
  model->BeginExtensiveChanges();

  // A parent to hold nodes temporarily orphaned by parent deletion.  It is
  // created only if it is needed.
  const BookmarkNode* foster_parent = NULL;

  // Iterate over the deletions, which are always at the front of the list.
  ChangeRecordList::const_iterator it;
  for (it = changes.Get().begin();
       it != changes.Get().end() && it->action == ChangeRecord::ACTION_DELETE;
       ++it) {
    const BookmarkNode* dst =
        model_associator_->GetChromeNodeFromSyncId(it->id);

    // Ignore changes to the permanent top-level nodes.  We only care about
    // their children.
    if (model->is_permanent_node(dst))
      continue;

    // Can't do anything if we can't find the chrome node.
    if (!dst)
      continue;

    // Children of a deleted node should not be deleted; they may be
    // reparented by a later change record.  Move them to a temporary place.
    if (!dst->empty()) {
      if (!foster_parent) {
        foster_parent = model->AddFolder(model->other_node(),
                                         model->other_node()->child_count(),
                                         base::string16());
        if (!foster_parent) {
          error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
              "Failed to create foster parent.");
          return;
        }
      }
      for (int i = dst->child_count() - 1; i >= 0; --i) {
        model->Move(dst->GetChild(i), foster_parent,
                    foster_parent->child_count());
      }
    }
    DCHECK_EQ(dst->child_count(), 0) << "Node being deleted has children";

    model_associator_->Disassociate(it->id);

    const BookmarkNode* parent = dst->parent();
    int index = parent->GetIndexOf(dst);
    if (index > -1)
      model->Remove(parent, index);
  }

  // A map to keep track of some reordering work we defer until later.
  std::multimap<int, const BookmarkNode*> to_reposition;

  syncer::ReadNode synced_bookmarks(trans);
  int64 synced_bookmarks_id = syncer::kInvalidId;
  if (synced_bookmarks.InitByTagLookup(kMobileBookmarksTag) ==
      syncer::BaseNode::INIT_OK) {
    synced_bookmarks_id = synced_bookmarks.GetId();
  }

  // Continue iterating where the previous loop left off.
  for ( ; it != changes.Get().end(); ++it) {
    const BookmarkNode* dst =
        model_associator_->GetChromeNodeFromSyncId(it->id);

    // Ignore changes to the permanent top-level nodes.  We only care about
    // their children.
    if (model->is_permanent_node(dst))
      continue;

    // Because the Synced Bookmarks node can be created server side, it's
    // possible it'll arrive at the client as an update. In that case it won't
    // have been associated at startup, the GetChromeNodeFromSyncId call above
    // will return NULL, and we won't detect it as a permanent node, resulting
    // in us trying to create it here (which will fail). Therefore, we add
    // special logic here just to detect the Synced Bookmarks folder.
    if (synced_bookmarks_id != syncer::kInvalidId &&
        it->id == synced_bookmarks_id) {
      // This is a newly created Synced Bookmarks node. Associate it.
      model_associator_->Associate(model->mobile_node(), it->id);
      continue;
    }

    DCHECK_NE(it->action, ChangeRecord::ACTION_DELETE)
        << "We should have passed all deletes by this point.";

    syncer::ReadNode src(trans);
    if (src.InitByIdLookup(it->id) != syncer::BaseNode::INIT_OK) {
      error_handler()->OnSingleDatatypeUnrecoverableError(FROM_HERE,
          "ApplyModelChanges was passed a bad ID");
      return;
    }

    const BookmarkNode* parent =
        model_associator_->GetChromeNodeFromSyncId(src.GetParentId());
    if (!parent) {
      LOG(ERROR) << "Could not find parent of node being added/updated."
        << " Node title: " << src.GetTitle()
        << ", parent id = " << src.GetParentId();
      continue;
    }

    if (dst) {
      DCHECK(it->action == ChangeRecord::ACTION_UPDATE)
          << "ACTION_UPDATE should be seen if and only if the node is known.";
      UpdateBookmarkWithSyncData(src, model, dst, profile_);

      // Move all modified entries to the right.  We'll fix it later.
      model->Move(dst, parent, parent->child_count());
    } else {
      DCHECK(it->action == ChangeRecord::ACTION_ADD)
          << "ACTION_ADD should be seen if and only if the node is unknown.";

      dst = CreateBookmarkNode(&src,
                               parent,
                               model,
                               profile_,
                               parent->child_count());
      if (!dst) {
        // We ignore bookmarks we can't add. Chances are this is caused by
        // a bookmark that was not fully associated.
        LOG(ERROR) << "Failed to create bookmark node with title "
                   << src.GetTitle() + " and url "
                   << src.GetBookmarkSpecifics().url();
        continue;
      }
      model_associator_->Associate(dst, src.GetId());
    }

    to_reposition.insert(std::make_pair(src.GetPositionIndex(), dst));
    bookmark_model_->SetNodeSyncTransactionVersion(dst, model_version);
  }

  // When we added or updated bookmarks in the previous loop, we placed them to
  // the far right position.  Now we iterate over all these modified items in
  // sync order, left to right, moving them into their proper positions.
  for (std::multimap<int, const BookmarkNode*>::iterator it =
       to_reposition.begin(); it != to_reposition.end(); ++it) {
    const BookmarkNode* parent = it->second->parent();
    model->Move(it->second, parent, it->first);
  }

  // Clean up the temporary node.
  if (foster_parent) {
    // There should be no nodes left under the foster parent.
    DCHECK_EQ(foster_parent->child_count(), 0);
    model->Remove(foster_parent->parent(),
                  foster_parent->parent()->GetIndexOf(foster_parent));
    foster_parent = NULL;
  }

  // The visibility of the mobile node may need to change.
  model_associator_->UpdatePermanentNodeVisibility();

  // Notify UI intensive observers of BookmarkModel that all updates have been
  // applied, and that they may now be consumed. This prevents issues like the
  // one described in crbug.com/281562, where old and new items on the bookmarks
  // bar would overlap.
  model->EndExtensiveChanges();

  // We are now ready to hear about bookmarks changes again.
  model->AddObserver(this);

  // All changes are applied in bookmark model. Set transaction version on
  // bookmark model to mark as synced.
  model->SetNodeSyncTransactionVersion(model->root_node(), model_version);
}

// Static.
// Update a bookmark node with specified sync data.
void BookmarkChangeProcessor::UpdateBookmarkWithSyncData(
    const syncer::BaseNode& sync_node,
    BookmarkModel* model,
    const BookmarkNode* node,
    Profile* profile) {
  DCHECK_EQ(sync_node.GetIsFolder(), node->is_folder());
  const sync_pb::BookmarkSpecifics& specifics =
      sync_node.GetBookmarkSpecifics();
  if (!sync_node.GetIsFolder())
    model->SetURL(node, GURL(specifics.url()));
  model->SetTitle(node, base::UTF8ToUTF16(sync_node.GetTitle()));
  if (specifics.has_creation_time_us()) {
    model->SetDateAdded(
        node,
        base::Time::FromInternalValue(specifics.creation_time_us()));
  }
  SetBookmarkFavicon(&sync_node, node, model, profile);
  SetBookmarkMetaInfo(&sync_node, node, model);
}

// static
void BookmarkChangeProcessor::UpdateTransactionVersion(
    int64 new_version,
    BookmarkModel* model,
    const std::vector<const BookmarkNode*>& nodes) {
  if (new_version != syncer::syncable::kInvalidTransactionVersion) {
    model->SetNodeSyncTransactionVersion(model->root_node(), new_version);
    for (size_t i = 0; i < nodes.size(); ++i) {
      model->SetNodeSyncTransactionVersion(nodes[i], new_version);
    }
  }
}

// static
// Creates a bookmark node under the given parent node from the given sync
// node. Returns the newly created node.
const BookmarkNode* BookmarkChangeProcessor::CreateBookmarkNode(
    syncer::BaseNode* sync_node,
    const BookmarkNode* parent,
    BookmarkModel* model,
    Profile* profile,
    int index) {
  DCHECK(parent);

  const BookmarkNode* node;
  if (sync_node->GetIsFolder()) {
    node = model->AddFolder(
        parent, index, base::UTF8ToUTF16(sync_node->GetTitle()));
  } else {
    // 'creation_time_us' was added in m24. Assume a time of 0 means now.
    const sync_pb::BookmarkSpecifics& specifics =
        sync_node->GetBookmarkSpecifics();
    const int64 create_time_internal = specifics.creation_time_us();
    base::Time create_time = (create_time_internal == 0) ?
        base::Time::Now() : base::Time::FromInternalValue(create_time_internal);
    node = model->AddURLWithCreationTime(parent, index,
                                         base::UTF8ToUTF16(
                                             sync_node->GetTitle()),
                                         GURL(specifics.url()), create_time);
    if (node)
      SetBookmarkFavicon(sync_node, node, model, profile);
  }
  if (node)
    SetBookmarkMetaInfo(sync_node, node, model);
  return node;
}

// static
// Sets the favicon of the given bookmark node from the given sync node.
bool BookmarkChangeProcessor::SetBookmarkFavicon(
    const syncer::BaseNode* sync_node,
    const BookmarkNode* bookmark_node,
    BookmarkModel* bookmark_model,
    Profile* profile) {
  const sync_pb::BookmarkSpecifics& specifics =
      sync_node->GetBookmarkSpecifics();
  const std::string& icon_bytes_str = specifics.favicon();
  if (icon_bytes_str.empty())
    return false;

  scoped_refptr<base::RefCountedString> icon_bytes(
      new base::RefCountedString());
  icon_bytes->data().assign(icon_bytes_str);
  GURL icon_url(specifics.icon_url());

  // Old clients may not be syncing the favicon URL. If the icon URL is not
  // synced, use the page URL as a fake icon URL as it is guaranteed to be
  // unique.
  if (icon_url.is_empty())
    icon_url = bookmark_node->url();

  ApplyBookmarkFavicon(bookmark_node, profile, icon_url, icon_bytes);

  return true;
}

// static
void BookmarkChangeProcessor::SetBookmarkMetaInfo(
    const syncer::BaseNode* sync_node,
    const BookmarkNode* bookmark_node,
    BookmarkModel* bookmark_model) {
  const sync_pb::BookmarkSpecifics& specifics =
      sync_node->GetBookmarkSpecifics();
  BookmarkNode::MetaInfoMap meta_info_map;
  for (int i = 0; i < specifics.meta_info_size(); ++i) {
    meta_info_map[specifics.meta_info(i).key()] =
        specifics.meta_info(i).value();
  }
  bookmark_model->SetNodeMetaInfoMap(bookmark_node, meta_info_map);
}

// static
void BookmarkChangeProcessor::SetSyncNodeMetaInfo(
    const BookmarkNode* node,
    syncer::WriteNode* sync_node) {
  sync_pb::BookmarkSpecifics specifics = sync_node->GetBookmarkSpecifics();
  specifics.clear_meta_info();
  const BookmarkNode::MetaInfoMap* meta_info_map = node->GetMetaInfoMap();
  if (meta_info_map) {
    for (BookmarkNode::MetaInfoMap::const_iterator it = meta_info_map->begin();
        it != meta_info_map->end(); ++it) {
      sync_pb::MetaInfo* meta_info = specifics.add_meta_info();
      meta_info->set_key(it->first);
      meta_info->set_value(it->second);
    }
  }
  sync_node->SetBookmarkSpecifics(specifics);
}

// static
void BookmarkChangeProcessor::ApplyBookmarkFavicon(
    const BookmarkNode* bookmark_node,
    Profile* profile,
    const GURL& icon_url,
    const scoped_refptr<base::RefCountedMemory>& bitmap_data) {
  HistoryService* history =
      HistoryServiceFactory::GetForProfile(profile, Profile::EXPLICIT_ACCESS);
  FaviconService* favicon_service =
      FaviconServiceFactory::GetForProfile(profile, Profile::EXPLICIT_ACCESS);

  history->AddPageNoVisitForBookmark(bookmark_node->url(),
                                     bookmark_node->GetTitle());
  // The client may have cached the favicon at 2x. Use MergeFavicon() as not to
  // overwrite the cached 2x favicon bitmap. Sync favicons are always
  // gfx::kFaviconSize in width and height. Store the favicon into history
  // as such.
  gfx::Size pixel_size(gfx::kFaviconSize, gfx::kFaviconSize);
  favicon_service->MergeFavicon(bookmark_node->url(),
                                icon_url,
                                chrome::FAVICON,
                                bitmap_data,
                                pixel_size);
}

// static
void BookmarkChangeProcessor::SetSyncNodeFavicon(
    const BookmarkNode* bookmark_node,
    BookmarkModel* model,
    syncer::WriteNode* sync_node) {
  scoped_refptr<base::RefCountedMemory> favicon_bytes(NULL);
  EncodeFavicon(bookmark_node, model, &favicon_bytes);
  if (favicon_bytes.get() && favicon_bytes->size()) {
    sync_pb::BookmarkSpecifics updated_specifics(
        sync_node->GetBookmarkSpecifics());
    updated_specifics.set_favicon(favicon_bytes->front(),
                                  favicon_bytes->size());
    updated_specifics.set_icon_url(bookmark_node->icon_url().spec());
    sync_node->SetBookmarkSpecifics(updated_specifics);
  }
}

}  // namespace browser_sync