root/chrome/browser/history/expire_history_backend.cc

DEFINITIONS

1. Read
2. Read
3. ShouldArchiveVisit
4. bookmark_service_
5. SetDatabases
6. DeleteURL
7. DeleteURLs
8. ExpireHistoryBetween
9. ExpireHistoryForTimes
10. ExpireVisits
11. ArchiveHistoryBefore
12. InitWorkQueue
13. GetAllVisitsReader
14. GetAutoSubframeVisitsReader
15. StartArchivingOldStuff
16. DeleteFaviconsIfPossible
17. BroadcastDeleteNotifications
18. DeleteVisitRelatedInfo
19. DeleteOneURL
20. ArchiveOneURL
21. ExpireURLsForVisits
22. ArchiveURLsAndVisits
23. ScheduleArchive
24. DoArchiveIteration
25. ArchiveSomeOldHistory
26. ParanoidExpireHistory
27. GetBookmarkService

// Copyright (c) 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/history/expire_history_backend.h"

#include <algorithm>
#include <functional>
#include <limits>

#include "base/bind.h"
#include "base/compiler_specific.h"
#include "base/file_util.h"
#include "base/files/file_enumerator.h"
#include "base/logging.h"
#include "base/message_loop/message_loop.h"
#include "chrome/browser/bookmarks/bookmark_service.h"
#include "chrome/browser/chrome_notification_types.h"
#include "chrome/browser/history/archived_database.h"
#include "chrome/browser/history/history_database.h"
#include "chrome/browser/history/history_notifications.h"
#include "chrome/browser/history/thumbnail_database.h"

using base::Time;
using base::TimeDelta;

namespace history {

namespace {

// The number of days by which the expiration threshold is advanced for items
// that we want to expire early, such as those of AUTO_SUBFRAME transition type.
//
// Early expiration stuff is kept around only for edge cases, as subframes
// don't appear in history and the vast majority of them are ads anyway. The
// main use case for these is if you're on a site with links to different
// frames, you'll be able to see those links as visited, and we'll also be
// able to get redirect information for those URLs.
//
// But since these uses are most valuable when you're actually on the site,
// and because these can take up the bulk of your history, we get a lot of
// space savings by deleting them quickly.
const int kEarlyExpirationAdvanceDays = 3;

// Reads all types of visits starting from beginning of time to the given end
// time. This is the most general reader.
class AllVisitsReader : public ExpiringVisitsReader {
 public:
  virtual bool Read(Time end_time, HistoryDatabase* db,
                    VisitVector* visits, int max_visits) const OVERRIDE {
    DCHECK(db) << "must have a database to operate upon";
    DCHECK(visits) << "visit vector has to exist in order to populate it";

    db->GetAllVisitsInRange(Time(), end_time, max_visits, visits);
    // When we got the maximum number of visits we asked for, we say there could
    // be additional things to expire now.
    return static_cast<int>(visits->size()) == max_visits;
  }
};

// Reads only AUTO_SUBFRAME visits, within a computed range. The range is
// computed as follows:
// * |begin_time| is read from the meta table. This value is updated whenever
//   there are no more additional visits to expire by this reader.
// * |end_time| is advanced forward by a constant (kEarlyExpirationAdvanceDay),
//   but not past the current time.
class AutoSubframeVisitsReader : public ExpiringVisitsReader {
 public:
  virtual bool Read(Time end_time, HistoryDatabase* db,
                    VisitVector* visits, int max_visits) const OVERRIDE {
    DCHECK(db) << "must have a database to operate upon";
    DCHECK(visits) << "visit vector has to exist in order to populate it";

    Time begin_time = db->GetEarlyExpirationThreshold();
    // Advance |end_time| to expire early.
    Time early_end_time = end_time +
        TimeDelta::FromDays(kEarlyExpirationAdvanceDays);

    // We don't want to set the early expiration threshold to a time in the
    // future.
    Time now = Time::Now();
    if (early_end_time > now)
      early_end_time = now;

    db->GetVisitsInRangeForTransition(begin_time, early_end_time,
                                      max_visits,
                                      content::PAGE_TRANSITION_AUTO_SUBFRAME,
                                      visits);
    bool more = static_cast<int>(visits->size()) == max_visits;
    if (!more)
      db->UpdateEarlyExpirationThreshold(early_end_time);

    return more;
  }
};

// Returns true if this visit is worth archiving. Otherwise, this visit is not
// worth saving (for example, subframe navigations and redirects) and we can
// just delete it when it gets old.
bool ShouldArchiveVisit(const VisitRow& visit) {
  int no_qualifier = content::PageTransitionStripQualifier(visit.transition);

  // These types of transitions are always "important" and the user will want
  // to see them.
  if (no_qualifier == content::PAGE_TRANSITION_TYPED ||
      no_qualifier == content::PAGE_TRANSITION_AUTO_BOOKMARK ||
      no_qualifier == content::PAGE_TRANSITION_AUTO_TOPLEVEL)
    return true;

  // Only archive these "less important" transitions when they were the final
  // navigation and not part of a redirect chain.
  if ((no_qualifier == content::PAGE_TRANSITION_LINK ||
       no_qualifier == content::PAGE_TRANSITION_FORM_SUBMIT ||
       no_qualifier == content::PAGE_TRANSITION_KEYWORD ||
       no_qualifier == content::PAGE_TRANSITION_GENERATED) &&
      visit.transition & content::PAGE_TRANSITION_CHAIN_END)
    return true;

  // The transition types we ignore are AUTO_SUBFRAME and MANUAL_SUBFRAME.
  return false;
}

// The number of visits we will expire very time we check for old items. This
// Prevents us from doing too much work any given time.
const int kNumExpirePerIteration = 32;

// The number of seconds between checking for items that should be expired when
// we think there might be more items to expire. This timeout is used when the
// last expiration found at least kNumExpirePerIteration and we want to check
// again "soon."
const int kExpirationDelaySec = 30;

// The number of minutes between checking, as with kExpirationDelaySec, but
// when we didn't find enough things to expire last time. If there was no
// history to expire last iteration, it's likely there is nothing next
// iteration, so we want to wait longer before checking to avoid wasting CPU.
const int kExpirationEmptyDelayMin = 5;

}  // namespace

struct ExpireHistoryBackend::DeleteDependencies {
  // The time range affected. These can be is_null() to be unbounded in one
  // or both directions.
  base::Time begin_time, end_time;

  // ----- Filled by DeleteVisitRelatedInfo or manually if a function doesn't
  //       call that function. -----

  // The unique URL rows affected by this delete.
  std::map<URLID, URLRow> affected_urls;

  // ----- Filled by DeleteOneURL -----

  // The URLs deleted during this operation.
  URLRows deleted_urls;

  // The list of all favicon IDs that the affected URLs had. Favicons will be
  // shared between all URLs with the same favicon, so this is the set of IDs
  // that we will need to check when the delete operations are complete.
  std::set<chrome::FaviconID> affected_favicons;

  // The list of all favicon urls that were actually deleted from the thumbnail
  // db.
  std::set<GURL> expired_favicons;
};

ExpireHistoryBackend::ExpireHistoryBackend(
    BroadcastNotificationDelegate* delegate,
    BookmarkService* bookmark_service)
    : delegate_(delegate),
      main_db_(NULL),
      archived_db_(NULL),
      thumb_db_(NULL),
      weak_factory_(this),
      bookmark_service_(bookmark_service) {
}

ExpireHistoryBackend::~ExpireHistoryBackend() {
}

void ExpireHistoryBackend::SetDatabases(HistoryDatabase* main_db,
                                        ArchivedDatabase* archived_db,
                                        ThumbnailDatabase* thumb_db) {
  main_db_ = main_db;
  archived_db_ = archived_db;
  thumb_db_ = thumb_db;
}

void ExpireHistoryBackend::DeleteURL(const GURL& url) {
  DeleteURLs(std::vector<GURL>(1, url));
}

void ExpireHistoryBackend::DeleteURLs(const std::vector<GURL>& urls) {
  if (!main_db_)
    return;

  DeleteDependencies dependencies;
  for (std::vector<GURL>::const_iterator url = urls.begin(); url != urls.end();
       ++url) {
    URLRow url_row;
    if (!main_db_->GetRowForURL(*url, &url_row))
      continue;  // Nothing to delete.

    // Collect all the visits and delete them. Note that we don't give
    // up if there are no visits, since the URL could still have an
    // entry that we should delete.  TODO(brettw): bug 1171148: We
    // should also delete from the archived DB.
    VisitVector visits;
    main_db_->GetVisitsForURL(url_row.id(), &visits);

    DeleteVisitRelatedInfo(visits, &dependencies);

    // We skip ExpireURLsForVisits (since we are deleting from the
    // URL, and not starting with visits in a given time range). We
    // therefore need to call the deletion and favicon update
    // functions manually.

    BookmarkService* bookmark_service = GetBookmarkService();
    bool is_bookmarked =
        (bookmark_service && bookmark_service->IsBookmarked(*url));

    DeleteOneURL(url_row, is_bookmarked, &dependencies);
  }

  DeleteFaviconsIfPossible(dependencies.affected_favicons,
                           &dependencies.expired_favicons);

  BroadcastDeleteNotifications(&dependencies, DELETION_USER_INITIATED);
}

void ExpireHistoryBackend::ExpireHistoryBetween(
    const std::set<GURL>& restrict_urls, Time begin_time, Time end_time) {
  if (!main_db_)
    return;

  // Find the affected visits and delete them.
  // TODO(brettw): bug 1171164: We should query the archived database here, too.
  VisitVector visits;
  main_db_->GetAllVisitsInRange(begin_time, end_time, 0, &visits);
  if (!restrict_urls.empty()) {
    std::set<URLID> url_ids;
    for (std::set<GURL>::const_iterator url = restrict_urls.begin();
        url != restrict_urls.end(); ++url)
      url_ids.insert(main_db_->GetRowForURL(*url, NULL));
    VisitVector all_visits;
    all_visits.swap(visits);
    for (VisitVector::iterator visit = all_visits.begin();
         visit != all_visits.end(); ++visit) {
      if (url_ids.find(visit->url_id) != url_ids.end())
        visits.push_back(*visit);
    }
  }
  ExpireVisits(visits);
}

void ExpireHistoryBackend::ExpireHistoryForTimes(
    const std::vector<base::Time>& times) {
  // |times| must be in reverse chronological order and have no
  // duplicates, i.e. each member must be earlier than the one before
  // it.
  DCHECK(
      std::adjacent_find(
          times.begin(), times.end(), std::less_equal<base::Time>()) ==
      times.end());

  if (!main_db_)
    return;

  // Find the affected visits and delete them.
  // TODO(brettw): bug 1171164: We should query the archived database here, too.
  VisitVector visits;
  main_db_->GetVisitsForTimes(times, &visits);
  ExpireVisits(visits);
}

void ExpireHistoryBackend::ExpireVisits(const VisitVector& visits) {
  if (visits.empty())
    return;

  DeleteDependencies dependencies;
  DeleteVisitRelatedInfo(visits, &dependencies);

  // Delete or update the URLs affected. We want to update the visit counts
  // since this is called by the user who wants to delete their recent history,
  // and we don't want to leave any evidence.
  ExpireURLsForVisits(visits, &dependencies);
  DeleteFaviconsIfPossible(dependencies.affected_favicons,
                           &dependencies.expired_favicons);

  // An is_null begin time means that all history should be deleted.
  BroadcastDeleteNotifications(&dependencies, DELETION_USER_INITIATED);

  // Pick up any bits possibly left over.
  ParanoidExpireHistory();
}

void ExpireHistoryBackend::ArchiveHistoryBefore(Time end_time) {
  if (!main_db_)
    return;

  // Archive as much history as possible before the given date.
  ArchiveSomeOldHistory(end_time, GetAllVisitsReader(),
                        std::numeric_limits<int>::max());
  ParanoidExpireHistory();
}

void ExpireHistoryBackend::InitWorkQueue() {
  DCHECK(work_queue_.empty()) << "queue has to be empty prior to init";

  for (size_t i = 0; i < readers_.size(); i++)
    work_queue_.push(readers_[i]);
}

const ExpiringVisitsReader* ExpireHistoryBackend::GetAllVisitsReader() {
  if (!all_visits_reader_)
    all_visits_reader_.reset(new AllVisitsReader());
  return all_visits_reader_.get();
}

const ExpiringVisitsReader*
    ExpireHistoryBackend::GetAutoSubframeVisitsReader() {
  if (!auto_subframe_visits_reader_)
    auto_subframe_visits_reader_.reset(new AutoSubframeVisitsReader());
  return auto_subframe_visits_reader_.get();
}

void ExpireHistoryBackend::StartArchivingOldStuff(
    TimeDelta expiration_threshold) {
  expiration_threshold_ = expiration_threshold;

  // Remove all readers, just in case this was method was called before.
  readers_.clear();
  // For now, we explicitly add all known readers. If we come up with more
  // reader types (in case we want to expire different types of visits in
  // different ways), we can make it be populated by creator/owner of
  // ExpireHistoryBackend.
  readers_.push_back(GetAllVisitsReader());
  readers_.push_back(GetAutoSubframeVisitsReader());

  // Initialize the queue with all tasks for the first set of iterations.
  InitWorkQueue();
  ScheduleArchive();
}

void ExpireHistoryBackend::DeleteFaviconsIfPossible(
    const std::set<chrome::FaviconID>& favicon_set,
    std::set<GURL>* expired_favicons) {
  if (!thumb_db_)
    return;

  for (std::set<chrome::FaviconID>::const_iterator i = favicon_set.begin();
       i != favicon_set.end(); ++i) {
    if (!thumb_db_->HasMappingFor(*i)) {
      GURL icon_url;
      chrome::IconType icon_type;
      if (thumb_db_->GetFaviconHeader(*i,
                                      &icon_url,
                                      &icon_type) &&
          thumb_db_->DeleteFavicon(*i)) {
        expired_favicons->insert(icon_url);
      }
    }
  }
}

void ExpireHistoryBackend::BroadcastDeleteNotifications(
    DeleteDependencies* dependencies, DeletionType type) {
  if (!dependencies->deleted_urls.empty()) {
    // Broadcast the URL deleted notification. Note that we also broadcast when
    // we were requested to delete everything even if that was a NOP, since
    // some components care to know when history is deleted (it's up to them to
    // determine if they care whether anything was deleted).
    scoped_ptr<URLsDeletedDetails> details(new URLsDeletedDetails);
    details->all_history = false;
    details->archived = (type == DELETION_ARCHIVED);
    details->rows = dependencies->deleted_urls;
    details->favicon_urls = dependencies->expired_favicons;
    delegate_->NotifySyncURLsDeleted(false, details->archived, &details->rows);
    delegate_->BroadcastNotifications(chrome::NOTIFICATION_HISTORY_URLS_DELETED,
                                      details.PassAs<HistoryDetails>());
  }
}

void ExpireHistoryBackend::DeleteVisitRelatedInfo(
    const VisitVector& visits,
    DeleteDependencies* dependencies) {
  for (size_t i = 0; i < visits.size(); i++) {
    // Delete the visit itself.
    main_db_->DeleteVisit(visits[i]);

    // Add the URL row to the affected URL list.
    std::map<URLID, URLRow>::const_iterator found =
        dependencies->affected_urls.find(visits[i].url_id);
    if (found == dependencies->affected_urls.end()) {
      URLRow row;
      if (!main_db_->GetURLRow(visits[i].url_id, &row))
        continue;
      dependencies->affected_urls[visits[i].url_id] = row;
    }
  }
}

void ExpireHistoryBackend::DeleteOneURL(
    const URLRow& url_row,
    bool is_bookmarked,
    DeleteDependencies* dependencies) {
  main_db_->DeleteSegmentForURL(url_row.id());

  if (!is_bookmarked) {
    dependencies->deleted_urls.push_back(url_row);

    // Delete stuff that references this URL.
    if (thumb_db_) {
      // Collect shared information.
      std::vector<IconMapping> icon_mappings;
      if (thumb_db_->GetIconMappingsForPageURL(url_row.url(), &icon_mappings)) {
        for (std::vector<IconMapping>::iterator m = icon_mappings.begin();
             m != icon_mappings.end(); ++m) {
          dependencies->affected_favicons.insert(m->icon_id);
        }
        // Delete the mapping entries for the url.
        thumb_db_->DeleteIconMappings(url_row.url());
      }
    }
    // Last, delete the URL entry.
    main_db_->DeleteURLRow(url_row.id());
  }
}

URLID ExpireHistoryBackend::ArchiveOneURL(const URLRow& url_row) {
  if (!archived_db_)
    return 0;

  // See if this URL is present in the archived database already. Note that
  // we must look up by ID since the URL ID will be different.
  URLRow archived_row;
  if (archived_db_->GetRowForURL(url_row.url(), &archived_row)) {
    // TODO(sky): bug 1168470, need to archive past search terms.
    // TODO(brettw): should be copy the visit counts over? This will mean that
    // the main DB's visit counts are only for the last 3 months rather than
    // accumulative.
    archived_row.set_last_visit(url_row.last_visit());
    archived_db_->UpdateURLRow(archived_row.id(), archived_row);
    return archived_row.id();
  }

  // This row is not in the archived DB, add it.
  return archived_db_->AddURL(url_row);
}

namespace {

struct ChangedURL {
  ChangedURL() : visit_count(0), typed_count(0) {}
  int visit_count;
  int typed_count;
};

}  // namespace

void ExpireHistoryBackend::ExpireURLsForVisits(
    const VisitVector& visits,
    DeleteDependencies* dependencies) {
  // First find all unique URLs and the number of visits we're deleting for
  // each one.
  std::map<URLID, ChangedURL> changed_urls;
  for (size_t i = 0; i < visits.size(); i++) {
    ChangedURL& cur = changed_urls[visits[i].url_id];
    // NOTE: This code must stay in sync with HistoryBackend::AddPageVisit().
    // TODO(pkasting): http://b/1148304 We shouldn't be marking so many URLs as
    // typed, which would help eliminate the need for this code (we still would
    // need to handle RELOAD transitions specially, though).
    content::PageTransition transition =
        content::PageTransitionStripQualifier(visits[i].transition);
    if (transition != content::PAGE_TRANSITION_RELOAD)
      cur.visit_count++;
    if ((transition == content::PAGE_TRANSITION_TYPED &&
        !content::PageTransitionIsRedirect(visits[i].transition)) ||
        transition == content::PAGE_TRANSITION_KEYWORD_GENERATED)
      cur.typed_count++;
  }

  // Check each unique URL with deleted visits.
  BookmarkService* bookmark_service = GetBookmarkService();
  for (std::map<URLID, ChangedURL>::const_iterator i = changed_urls.begin();
       i != changed_urls.end(); ++i) {
    // The unique URL rows should already be filled into the dependencies.
    URLRow& url_row = dependencies->affected_urls[i->first];
    if (!url_row.id())
      continue;  // URL row doesn't exist in the database.

    // Check if there are any other visits for this URL and update the time
    // (the time change may not actually be synced to disk below when we're
    // archiving).
    VisitRow last_visit;
    if (main_db_->GetMostRecentVisitForURL(url_row.id(), &last_visit))
      url_row.set_last_visit(last_visit.visit_time);
    else
      url_row.set_last_visit(Time());

    // Don't delete URLs with visits still in the DB, or bookmarked.
    bool is_bookmarked =
        (bookmark_service && bookmark_service->IsBookmarked(url_row.url()));
    if (!is_bookmarked && url_row.last_visit().is_null()) {
      // Not bookmarked and no more visits. Nuke the url.
      DeleteOneURL(url_row, is_bookmarked, dependencies);
    } else {
      // NOTE: The calls to std::max() below are a backstop, but they should
      // never actually be needed unless the database is corrupt (I think).
      url_row.set_visit_count(
          std::max(0, url_row.visit_count() - i->second.visit_count));
      url_row.set_typed_count(
          std::max(0, url_row.typed_count() - i->second.typed_count));

      // Update the db with the new details.
      main_db_->UpdateURLRow(url_row.id(), url_row);
    }
  }
}

void ExpireHistoryBackend::ArchiveURLsAndVisits(
    const VisitVector& visits,
    DeleteDependencies* dependencies) {
  if (!archived_db_ || !main_db_)
    return;

  // Make sure all unique URL rows are added to the dependency list and the
  // archived database. We will also keep the mapping between the main DB URLID
  // and the archived one.
  std::map<URLID, URLID> main_id_to_archived_id;
  for (size_t i = 0; i < visits.size(); i++) {
    std::map<URLID, URLRow>::const_iterator found =
      dependencies->affected_urls.find(visits[i].url_id);
    if (found == dependencies->affected_urls.end()) {
      // Unique URL encountered, archive it.
      URLRow row;  // Row in the main DB.
      URLID archived_id;  // ID in the archived DB.
      if (!main_db_->GetURLRow(visits[i].url_id, &row) ||
          !(archived_id = ArchiveOneURL(row))) {
        // Failure archiving, skip this one.
        continue;
      }

      // Only add URL to the dependency list once we know we successfully
      // archived it.
      main_id_to_archived_id[row.id()] = archived_id;
      dependencies->affected_urls[row.id()] = row;
    }
  }

  // Retrieve the sources for all the archived visits before archiving.
  // The returned visit_sources vector should contain the source for each visit
  // from visits at the same index.
  VisitSourceMap visit_sources;
  main_db_->GetVisitsSource(visits, &visit_sources);

  // Now archive the visits since we know the URL ID to make them reference.
  // The source visit list should still reference the visits in the main DB, but
  // we will update it to reflect only the visits that were successfully
  // archived.
  for (size_t i = 0; i < visits.size(); i++) {
    // Construct the visit that we will add to the archived database. We do
    // not store referring visits since we delete many of the visits when
    // archiving.
    VisitRow cur_visit(visits[i]);
    cur_visit.url_id = main_id_to_archived_id[cur_visit.url_id];
    cur_visit.referring_visit = 0;
    VisitSourceMap::iterator iter = visit_sources.find(visits[i].visit_id);
    archived_db_->AddVisit(
        &cur_visit,
        iter == visit_sources.end() ? SOURCE_BROWSED : iter->second);
    // Ignore failures, we will delete it from the main DB no matter what.
  }
}

void ExpireHistoryBackend::ScheduleArchive() {
  TimeDelta delay;
  if (work_queue_.empty()) {
    // If work queue is empty, reset the work queue to contain all tasks and
    // schedule next iteration after a longer delay.
    InitWorkQueue();
    delay = TimeDelta::FromMinutes(kExpirationEmptyDelayMin);
  } else {
    delay = TimeDelta::FromSeconds(kExpirationDelaySec);
  }

  base::MessageLoop::current()->PostDelayedTask(
      FROM_HERE,
      base::Bind(&ExpireHistoryBackend::DoArchiveIteration,
                 weak_factory_.GetWeakPtr()),
      delay);
}

void ExpireHistoryBackend::DoArchiveIteration() {
  DCHECK(!work_queue_.empty()) << "queue has to be non-empty";

  const ExpiringVisitsReader* reader = work_queue_.front();
  bool more_to_expire = ArchiveSomeOldHistory(GetCurrentArchiveTime(), reader,
                                              kNumExpirePerIteration);

  work_queue_.pop();
  // If there are more items to expire, add the reader back to the queue, thus
  // creating a new task for future iterations.
  if (more_to_expire)
    work_queue_.push(reader);

  ScheduleArchive();
}

bool ExpireHistoryBackend::ArchiveSomeOldHistory(
    base::Time end_time,
    const ExpiringVisitsReader* reader,
    int max_visits) {
  if (!main_db_)
    return false;

  // Add an extra time unit to given end time, because
  // GetAllVisitsInRange, et al. queries' end value is non-inclusive.
  Time effective_end_time =
      Time::FromInternalValue(end_time.ToInternalValue() + 1);

  VisitVector affected_visits;
  bool more_to_expire = reader->Read(effective_end_time, main_db_,
                                     &affected_visits, max_visits);

  // Some visits we'll delete while others we'll archive.
  VisitVector deleted_visits, archived_visits;
  for (size_t i = 0; i < affected_visits.size(); i++) {
    if (ShouldArchiveVisit(affected_visits[i]))
      archived_visits.push_back(affected_visits[i]);
    else
      deleted_visits.push_back(affected_visits[i]);
  }

  // Do the actual archiving.
  DeleteDependencies archived_dependencies;
  ArchiveURLsAndVisits(archived_visits, &archived_dependencies);
  DeleteVisitRelatedInfo(archived_visits, &archived_dependencies);

  DeleteDependencies deleted_dependencies;
  DeleteVisitRelatedInfo(deleted_visits, &deleted_dependencies);

  // This will remove or archive all the affected URLs. Must do the deleting
  // cleanup before archiving so the delete dependencies structure references
  // only those URLs that were actually deleted instead of having some visits
  // archived and then the rest deleted.
  ExpireURLsForVisits(deleted_visits, &deleted_dependencies);
  ExpireURLsForVisits(archived_visits, &archived_dependencies);

  // Create a union of all affected favicons (we don't store favicons for
  // archived URLs) and delete them.
  std::set<chrome::FaviconID> affected_favicons(
      archived_dependencies.affected_favicons);
  for (std::set<chrome::FaviconID>::const_iterator i =
           deleted_dependencies.affected_favicons.begin();
       i != deleted_dependencies.affected_favicons.end(); ++i) {
    affected_favicons.insert(*i);
  }
  DeleteFaviconsIfPossible(affected_favicons,
                           &deleted_dependencies.expired_favicons);

  // Send notifications for the stuff that was deleted. These won't normally be
  // in history views since they were subframes, but they will be in the visited
  // link system, which needs to be updated now. This function is smart enough
  // to not do anything if nothing was deleted.
  BroadcastDeleteNotifications(&deleted_dependencies, DELETION_ARCHIVED);

  return more_to_expire;
}

void ExpireHistoryBackend::ParanoidExpireHistory() {
  // TODO(brettw): Bug 1067331: write this to clean up any errors.
}

BookmarkService* ExpireHistoryBackend::GetBookmarkService() {
  // We use the bookmark service to determine if a URL is bookmarked. The
  // bookmark service is loaded on a separate thread and may not be done by the
  // time we get here. We therefor block until the bookmarks have finished
  // loading.
  if (bookmark_service_)
    bookmark_service_->BlockTillLoaded();
  return bookmark_service_;
}

}  // namespace history