root/chrome/browser/character_encoding.cc

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DEFINITIONS

This source file includes following definitions.
  1. locale_dependent_encoding_ids
  2. current_display_encodings
  3. GetIdToCanonicalEncodingNameMapData
  4. GetCanonicalEncodingNameToIdMapData
  5. GetCanonicalNameDisplayNameMapData
  6. CanonicalEncodingMapSingleton
  7. ParseEncodingListSeparatedWithComma
  8. GetEncodingDisplayName
  9. GetEncodingCategoryStringIdByCommandId
  10. GetEncodingCategoryStringByCommandId
  11. GetCommandIdByCanonicalEncodingName
  12. GetCanonicalEncodingNameByCommandId
  13. GetCanonicalEncodingDisplayNameByCommandId
  14. GetSupportCanonicalEncodingCount
  15. GetCanonicalEncodingNameByIndex
  16. GetCanonicalEncodingDisplayNameByIndex
  17. GetEncodingCommandIdByIndex
  18. GetCanonicalEncodingNameByAliasName
  19. GetCurrentDisplayEncodings
  20. UpdateRecentlySelectedEncoding

// 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/character_encoding.h"

#include <map>
#include <set>

#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/strings/string_tokenizer.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "chrome/app/chrome_command_ids.h"
#include "content/public/browser/browser_thread.h"
#include "grit/generated_resources.h"
#include "third_party/icu/source/common/unicode/ucnv.h"
#include "ui/base/l10n/l10n_util.h"
#include "ui/base/l10n/l10n_util_collator.h"

using content::BrowserThread;

namespace {

// The maximum length of short list of recently user selected encodings is 3.
const size_t kUserSelectedEncodingsMaxLength = 3;

typedef struct {
  int resource_id;
  const char* name;
  int category_string_id;
} CanonicalEncodingData;

// An array of all supported canonical encoding names.
const CanonicalEncodingData kCanonicalEncodingNames[] = {
  { IDC_ENCODING_UTF8, "UTF-8", IDS_ENCODING_UNICODE },
  { IDC_ENCODING_UTF16LE, "UTF-16LE", IDS_ENCODING_UNICODE },
  { IDC_ENCODING_ISO88591, "ISO-8859-1", IDS_ENCODING_WESTERN },
  { IDC_ENCODING_WINDOWS1252, "windows-1252", IDS_ENCODING_WESTERN },
  { IDC_ENCODING_GBK, "GBK", IDS_ENCODING_SIMP_CHINESE },
  { IDC_ENCODING_GB18030, "gb18030", IDS_ENCODING_SIMP_CHINESE },
  { IDC_ENCODING_BIG5, "Big5", IDS_ENCODING_TRAD_CHINESE },
  { IDC_ENCODING_BIG5HKSCS, "Big5-HKSCS", IDS_ENCODING_TRAD_CHINESE },
  { IDC_ENCODING_KOREAN, "EUC-KR", IDS_ENCODING_KOREAN },
  { IDC_ENCODING_SHIFTJIS, "Shift_JIS", IDS_ENCODING_JAPANESE },
  { IDC_ENCODING_EUCJP, "EUC-JP", IDS_ENCODING_JAPANESE },
  { IDC_ENCODING_ISO2022JP, "ISO-2022-JP", IDS_ENCODING_JAPANESE },
  { IDC_ENCODING_THAI, "windows-874", IDS_ENCODING_THAI },
  { IDC_ENCODING_ISO885915, "ISO-8859-15", IDS_ENCODING_WESTERN },
  { IDC_ENCODING_MACINTOSH, "macintosh", IDS_ENCODING_WESTERN },
  { IDC_ENCODING_ISO88592, "ISO-8859-2", IDS_ENCODING_CENTRAL_EUROPEAN },
  { IDC_ENCODING_WINDOWS1250, "windows-1250", IDS_ENCODING_CENTRAL_EUROPEAN },
  { IDC_ENCODING_ISO88595, "ISO-8859-5", IDS_ENCODING_CYRILLIC },
  { IDC_ENCODING_WINDOWS1251, "windows-1251", IDS_ENCODING_CYRILLIC },
  { IDC_ENCODING_KOI8R, "KOI8-R", IDS_ENCODING_CYRILLIC },
  { IDC_ENCODING_KOI8U, "KOI8-U", IDS_ENCODING_CYRILLIC },
  { IDC_ENCODING_ISO88597, "ISO-8859-7", IDS_ENCODING_GREEK },
  { IDC_ENCODING_WINDOWS1253, "windows-1253", IDS_ENCODING_GREEK },
  { IDC_ENCODING_WINDOWS1254, "windows-1254", IDS_ENCODING_TURKISH },
  { IDC_ENCODING_WINDOWS1256, "windows-1256", IDS_ENCODING_ARABIC },
  { IDC_ENCODING_ISO88596, "ISO-8859-6", IDS_ENCODING_ARABIC },
  { IDC_ENCODING_WINDOWS1255, "windows-1255", IDS_ENCODING_HEBREW },
  { IDC_ENCODING_ISO88598I, "ISO-8859-8-I", IDS_ENCODING_HEBREW },
  { IDC_ENCODING_ISO88598, "ISO-8859-8", IDS_ENCODING_HEBREW },
  { IDC_ENCODING_WINDOWS1258, "windows-1258", IDS_ENCODING_VIETNAMESE },
  { IDC_ENCODING_ISO88594, "ISO-8859-4", IDS_ENCODING_BALTIC },
  { IDC_ENCODING_ISO885913, "ISO-8859-13", IDS_ENCODING_BALTIC },
  { IDC_ENCODING_WINDOWS1257, "windows-1257", IDS_ENCODING_BALTIC },
  { IDC_ENCODING_ISO88593, "ISO-8859-3", IDS_ENCODING_SOUTH_EUROPEAN },
  { IDC_ENCODING_ISO885910, "ISO-8859-10", IDS_ENCODING_NORDIC },
  { IDC_ENCODING_ISO885914, "ISO-8859-14", IDS_ENCODING_CELTIC },
  { IDC_ENCODING_ISO885916, "ISO-8859-16", IDS_ENCODING_ROMANIAN },
};

const int kCanonicalEncodingNamesLength = arraysize(kCanonicalEncodingNames);

typedef std::map<int, std::pair<const char*, int> >
    IdToCanonicalEncodingNameMapType;
typedef std::map<const std::string, int> CanonicalEncodingNameToIdMapType;

typedef struct {
  const char* canonical_form;
  const char* display_form;
} CanonicalEncodingDisplayNamePair;

const CanonicalEncodingDisplayNamePair kCanonicalDisplayNameOverrides[] = {
  // Only lists the canonical names where we want a different form for display.
  { "macintosh", "Macintosh" },
  { "windows-874", "Windows-874" },
  { "windows-1250", "Windows-1250" },
  { "windows-1251", "Windows-1251" },
  { "windows-1252", "Windows-1252" },
  { "windows-1253", "Windows-1253" },
  { "windows-1254", "Windows-1254" },
  { "windows-1255", "Windows-1255" },
  { "windows-1256", "Windows-1256" },
  { "windows-1257", "Windows-1257" },
  { "windows-1258", "Windows-1258" },
};

const int kCanonicalDisplayNameOverridesLength =
    arraysize(kCanonicalDisplayNameOverrides);

typedef std::map<std::string, const char*> CanonicalNameDisplayNameMapType;

class CanonicalEncodingMap {
 public:
  CanonicalEncodingMap() {}
  const IdToCanonicalEncodingNameMapType* GetIdToCanonicalEncodingNameMapData();
  const CanonicalEncodingNameToIdMapType* GetCanonicalEncodingNameToIdMapData();
  const CanonicalNameDisplayNameMapType* GetCanonicalNameDisplayNameMapData();
  std::vector<int>* locale_dependent_encoding_ids() {
    return &locale_dependent_encoding_ids_;
  }

  std::vector<CharacterEncoding::EncodingInfo>* current_display_encodings() {
    return &current_display_encodings_;
  }

 private:
  scoped_ptr<IdToCanonicalEncodingNameMapType> id_to_encoding_name_map_;
  scoped_ptr<CanonicalEncodingNameToIdMapType> encoding_name_to_id_map_;
  scoped_ptr<CanonicalNameDisplayNameMapType>
      encoding_name_to_display_name_map_;
  std::vector<int> locale_dependent_encoding_ids_;
  std::vector<CharacterEncoding::EncodingInfo> current_display_encodings_;

  DISALLOW_COPY_AND_ASSIGN(CanonicalEncodingMap);
};

const IdToCanonicalEncodingNameMapType*
    CanonicalEncodingMap::GetIdToCanonicalEncodingNameMapData() {
  // Testing and building map is not thread safe, this function is supposed to
  // only run in UI thread. Myabe I should add a lock in here for making it as
  // thread safe.
  if (!id_to_encoding_name_map_.get()) {
    id_to_encoding_name_map_.reset(new IdToCanonicalEncodingNameMapType);
    for (int i = 0; i < kCanonicalEncodingNamesLength; ++i) {
      int resource_id = kCanonicalEncodingNames[i].resource_id;
      (*id_to_encoding_name_map_)[resource_id] =
        std::make_pair(kCanonicalEncodingNames[i].name,
                       kCanonicalEncodingNames[i].category_string_id);
    }
  }
  return id_to_encoding_name_map_.get();
}

const CanonicalEncodingNameToIdMapType*
    CanonicalEncodingMap::GetCanonicalEncodingNameToIdMapData() {
  if (!encoding_name_to_id_map_.get()) {
    encoding_name_to_id_map_.reset(new CanonicalEncodingNameToIdMapType);
    for (int i = 0; i < kCanonicalEncodingNamesLength; ++i) {
      (*encoding_name_to_id_map_)[kCanonicalEncodingNames[i].name] =
          kCanonicalEncodingNames[i].resource_id;
    }
  }
  return encoding_name_to_id_map_.get();
}

const CanonicalNameDisplayNameMapType*
    CanonicalEncodingMap::GetCanonicalNameDisplayNameMapData() {
  if (!encoding_name_to_display_name_map_.get()) {
    encoding_name_to_display_name_map_.reset(
        new CanonicalNameDisplayNameMapType);
    // First store the names in the kCanonicalEncodingNames list.
    for (int i = 0; i < kCanonicalEncodingNamesLength; ++i) {
      (*encoding_name_to_display_name_map_)[kCanonicalEncodingNames[i].name] =
          kCanonicalEncodingNames[i].name;
    }
    // Then save in the overrides.
    for (int i = 0; i < kCanonicalDisplayNameOverridesLength; ++i) {
      (*encoding_name_to_display_name_map_)
          [kCanonicalDisplayNameOverrides[i].canonical_form] =
          kCanonicalDisplayNameOverrides[i].display_form;
    }
    DCHECK(static_cast<int>(encoding_name_to_display_name_map_->size()) ==
           kCanonicalEncodingNamesLength)
        << "Got an override that wasn't in the encoding list";
  }
  return encoding_name_to_display_name_map_.get();
}

// A static map object which contains all resourceid-nonsequenced canonical
// encoding names.
CanonicalEncodingMap* CanonicalEncodingMapSingleton() {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
  static CanonicalEncodingMap* singleton = new CanonicalEncodingMap;
  return singleton;
}

const int kDefaultEncodingMenus[] = {
  IDC_ENCODING_UTF16LE,
  IDC_ENCODING_ISO88591,
  IDC_ENCODING_WINDOWS1252,
  IDC_ENCODING_GBK,
  IDC_ENCODING_GB18030,
  IDC_ENCODING_BIG5,
  IDC_ENCODING_BIG5HKSCS,
  IDC_ENCODING_KOREAN,
  IDC_ENCODING_SHIFTJIS,
  IDC_ENCODING_EUCJP,
  IDC_ENCODING_ISO2022JP,
  IDC_ENCODING_THAI,
  IDC_ENCODING_ISO885915,
  IDC_ENCODING_MACINTOSH,
  IDC_ENCODING_ISO88592,
  IDC_ENCODING_WINDOWS1250,
  IDC_ENCODING_ISO88595,
  IDC_ENCODING_WINDOWS1251,
  IDC_ENCODING_KOI8R,
  IDC_ENCODING_KOI8U,
  IDC_ENCODING_ISO88597,
  IDC_ENCODING_WINDOWS1253,
  IDC_ENCODING_WINDOWS1254,
  IDC_ENCODING_WINDOWS1256,
  IDC_ENCODING_ISO88596,
  IDC_ENCODING_WINDOWS1255,
  IDC_ENCODING_ISO88598I,
  IDC_ENCODING_ISO88598,
  IDC_ENCODING_WINDOWS1258,
  IDC_ENCODING_ISO88594,
  IDC_ENCODING_ISO885913,
  IDC_ENCODING_WINDOWS1257,
  IDC_ENCODING_ISO88593,
  IDC_ENCODING_ISO885910,
  IDC_ENCODING_ISO885914,
  IDC_ENCODING_ISO885916,
};

const int kDefaultEncodingMenusLength = arraysize(kDefaultEncodingMenus);

// Parse the input |encoding_list| which is a encoding list separated with
// comma, get available encoding ids and save them to |available_list|.
// The parameter |maximum_size| indicates maximum size of encoding items we
// want to get from the |encoding_list|.
void ParseEncodingListSeparatedWithComma(
    const std::string& encoding_list, std::vector<int>* const available_list,
    size_t maximum_size) {
  base::StringTokenizer tokenizer(encoding_list, ",");
  while (tokenizer.GetNext()) {
    int id = CharacterEncoding::GetCommandIdByCanonicalEncodingName(
        tokenizer.token());
    // Ignore invalid encoding.
    if (!id)
      continue;
    available_list->push_back(id);
    if (available_list->size() == maximum_size)
      return;
  }
}

base::string16 GetEncodingDisplayName(const std::string& encoding_name,
                                      int category_string_id) {
  base::string16 category_name = l10n_util::GetStringUTF16(category_string_id);
  if (category_string_id != IDS_ENCODING_KOREAN &&
      category_string_id != IDS_ENCODING_THAI &&
      category_string_id != IDS_ENCODING_TURKISH) {
    const CanonicalNameDisplayNameMapType* map =
        CanonicalEncodingMapSingleton()->GetCanonicalNameDisplayNameMapData();
    DCHECK(map);

    CanonicalNameDisplayNameMapType::const_iterator found_name =
        map->find(encoding_name);
    DCHECK(found_name != map->end());
    return l10n_util::GetStringFUTF16(IDS_ENCODING_DISPLAY_TEMPLATE,
                                      category_name,
                                      base::ASCIIToUTF16(found_name->second));
  }
  return category_name;
}

int GetEncodingCategoryStringIdByCommandId(int id) {
  const IdToCanonicalEncodingNameMapType* map =
      CanonicalEncodingMapSingleton()->GetIdToCanonicalEncodingNameMapData();
  DCHECK(map);

  IdToCanonicalEncodingNameMapType::const_iterator found_name = map->find(id);
  if (found_name != map->end())
    return found_name->second.second;
  return 0;
}

std::string GetEncodingCategoryStringByCommandId(int id) {
  int category_id = GetEncodingCategoryStringIdByCommandId(id);
  if (category_id)
    return l10n_util::GetStringUTF8(category_id);
  return std::string();
}

}  // namespace

CharacterEncoding::EncodingInfo::EncodingInfo(int id)
    : encoding_id(id) {
  encoding_category_name =
      base::UTF8ToUTF16(GetEncodingCategoryStringByCommandId(id));
  encoding_display_name = GetCanonicalEncodingDisplayNameByCommandId(id);
}

// Static.
int CharacterEncoding::GetCommandIdByCanonicalEncodingName(
    const std::string& encoding_name) {
  const CanonicalEncodingNameToIdMapType* map =
      CanonicalEncodingMapSingleton()->GetCanonicalEncodingNameToIdMapData();
  DCHECK(map);

  CanonicalEncodingNameToIdMapType::const_iterator found_id =
      map->find(encoding_name);
  if (found_id != map->end())
    return found_id->second;
  return 0;
}

// Static.
std::string CharacterEncoding::GetCanonicalEncodingNameByCommandId(int id) {
  const IdToCanonicalEncodingNameMapType* map =
      CanonicalEncodingMapSingleton()->GetIdToCanonicalEncodingNameMapData();
  DCHECK(map);

  IdToCanonicalEncodingNameMapType::const_iterator found_name = map->find(id);
  if (found_name != map->end())
    return found_name->second.first;
  return std::string();
}

// Static.
base::string16 CharacterEncoding::GetCanonicalEncodingDisplayNameByCommandId(
    int id) {
  const IdToCanonicalEncodingNameMapType* map =
      CanonicalEncodingMapSingleton()->GetIdToCanonicalEncodingNameMapData();
  DCHECK(map);

  IdToCanonicalEncodingNameMapType::const_iterator found_name = map->find(id);
  if (found_name != map->end())
    return GetEncodingDisplayName(found_name->second.first,
                                  found_name->second.second);
  return base::string16();
}

// Static.
// Return count number of all supported canonical encoding.
int CharacterEncoding::GetSupportCanonicalEncodingCount() {
  return kCanonicalEncodingNamesLength;
}

// Static.
std::string CharacterEncoding::GetCanonicalEncodingNameByIndex(int index) {
  if (index < kCanonicalEncodingNamesLength)
    return kCanonicalEncodingNames[index].name;
  return std::string();
}

// Static.
base::string16 CharacterEncoding::GetCanonicalEncodingDisplayNameByIndex(
    int index) {
  if (index < kCanonicalEncodingNamesLength)
    return GetEncodingDisplayName(kCanonicalEncodingNames[index].name,
        kCanonicalEncodingNames[index].category_string_id);
  return base::string16();
}

// Static.
int CharacterEncoding::GetEncodingCommandIdByIndex(int index) {
  if (index < kCanonicalEncodingNamesLength)
    return kCanonicalEncodingNames[index].resource_id;
  return 0;
}

// Static.
std::string CharacterEncoding::GetCanonicalEncodingNameByAliasName(
    const std::string& alias_name) {
  // If the input alias_name is already canonical encoding name, just return it.
  const CanonicalEncodingNameToIdMapType* map =
      CanonicalEncodingMapSingleton()->GetCanonicalEncodingNameToIdMapData();
  DCHECK(map);

  CanonicalEncodingNameToIdMapType::const_iterator found_id =
      map->find(alias_name);
  if (found_id != map->end())
    return alias_name;

  UErrorCode error_code = U_ZERO_ERROR;

  const char* canonical_name = ucnv_getCanonicalName(
      alias_name.c_str(), "MIME", &error_code);
  // If failed,  then try IANA next.
  if (U_FAILURE(error_code) || !canonical_name) {
    error_code = U_ZERO_ERROR;
    canonical_name = ucnv_getCanonicalName(
      alias_name.c_str(), "IANA", &error_code);
  }

  if (canonical_name) {
    // TODO(jnd) use a map to handle all customized {alias, canonical}
    // encoding mappings if we have more than one pair.
    // We don't want to add an unnecessary charset to the encoding menu, so we
    // alias 'US-ASCII' to 'ISO-8859-1' in our UI without touching WebKit.
    // http://crbug.com/15801.
    if (alias_name == "US-ASCII")
      return GetCanonicalEncodingNameByCommandId(IDC_ENCODING_ISO88591);
    return canonical_name;
  } else {
    return std::string();
  }
}

// Static
// According to the behavior of user recently selected encoding short list in
// Firefox, we always put UTF-8 as top position, after then put user
// recent selected encodings, then put local dependent encoding items.
// At last, we put all remaining encoding items.
const std::vector<CharacterEncoding::EncodingInfo>*
    CharacterEncoding::GetCurrentDisplayEncodings(
    const std::string& locale,
    const std::string& locale_encodings,
    const std::string& recently_select_encodings) {
  std::vector<int>* const locale_dependent_encoding_list =
      CanonicalEncodingMapSingleton()->locale_dependent_encoding_ids();
  std::vector<CharacterEncoding::EncodingInfo>* const encoding_list =
      CanonicalEncodingMapSingleton()->current_display_encodings();

  // Initialize locale dependent static encoding list.
  if (locale_dependent_encoding_list->empty() && !locale_encodings.empty())
    ParseEncodingListSeparatedWithComma(locale_encodings,
                                        locale_dependent_encoding_list,
                                        kUserSelectedEncodingsMaxLength);

  CR_DEFINE_STATIC_LOCAL(std::string, cached_user_selected_encodings, ());
  // Build current display encoding list.
  if (encoding_list->empty() ||
      cached_user_selected_encodings != recently_select_encodings) {
    // Update user recently selected encodings.
    cached_user_selected_encodings = recently_select_encodings;
    // Clear old encoding list since user recently selected encodings changed.
    encoding_list->clear();
    // Always add UTF-8 to first encoding position.
    encoding_list->push_back(EncodingInfo(IDC_ENCODING_UTF8));
    std::set<int> inserted_encoding;
    inserted_encoding.insert(IDC_ENCODING_UTF8);

    // Parse user recently selected encodings and get list
    std::vector<int> recently_select_encoding_list;
    ParseEncodingListSeparatedWithComma(recently_select_encodings,
                                        &recently_select_encoding_list,
                                        kUserSelectedEncodingsMaxLength);

    // Put 'cached encodings' (dynamic encoding list) after 'local dependent
    // encoding list'.
    recently_select_encoding_list.insert(recently_select_encoding_list.begin(),
        locale_dependent_encoding_list->begin(),
        locale_dependent_encoding_list->end());
    for (std::vector<int>::iterator it = recently_select_encoding_list.begin();
         it != recently_select_encoding_list.end(); ++it) {
        // Test whether we have met this encoding id.
        bool ok = inserted_encoding.insert(*it).second;
        // Duplicated encoding, ignore it. Ideally, this situation should not
        // happened, but just in case some one manually edit preference file.
        if (!ok)
          continue;
        encoding_list->push_back(EncodingInfo(*it));
    }
    // Append a separator;
    encoding_list->push_back(EncodingInfo(0));

    // We need to keep "Unicode (UTF-16LE)" always at the top (among the rest
    // of encodings) instead of being sorted along with other encodings. So if
    // "Unicode (UTF-16LE)" is already in previous encodings, sort the rest
    // of encodings. Otherwise Put "Unicode (UTF-16LE)" on the first of the
    // rest of encodings, skip "Unicode (UTF-16LE)" and sort all left encodings.
    int start_sorted_index = encoding_list->size();
    if (inserted_encoding.find(IDC_ENCODING_UTF16LE) ==
        inserted_encoding.end()) {
      encoding_list->push_back(EncodingInfo(IDC_ENCODING_UTF16LE));
      inserted_encoding.insert(IDC_ENCODING_UTF16LE);
      start_sorted_index++;
    }

    // Add the rest of encodings that are neither in the static encoding list
    // nor in the list of recently selected encodings.
    // Build the encoding list sorted in the current locale sorting order.
    for (int i = 0; i < kDefaultEncodingMenusLength; ++i) {
      int id = kDefaultEncodingMenus[i];
      // We have inserted this encoding, skip it.
      if (inserted_encoding.find(id) != inserted_encoding.end())
        continue;
      encoding_list->push_back(EncodingInfo(id));
    }
    // Sort the encoding list.
    l10n_util::SortVectorWithStringKey(locale,
                                       encoding_list,
                                       start_sorted_index,
                                       encoding_list->size(),
                                       true);
  }
  DCHECK(!encoding_list->empty());
  return encoding_list;
}

// Static
bool CharacterEncoding::UpdateRecentlySelectedEncoding(
    const std::string& original_selected_encodings,
    int new_selected_encoding_id,
    std::string* selected_encodings) {
  // Get encoding name.
  std::string encoding_name =
      GetCanonicalEncodingNameByCommandId(new_selected_encoding_id);
  DCHECK(!encoding_name.empty());
  // Check whether the new encoding is in local dependent encodings or original
  // recently selected encodings. If yes, do not add it.
  std::vector<int>* locale_dependent_encoding_list =
      CanonicalEncodingMapSingleton()->locale_dependent_encoding_ids();
  DCHECK(locale_dependent_encoding_list);
  std::vector<int> selected_encoding_list;
  ParseEncodingListSeparatedWithComma(original_selected_encodings,
                                      &selected_encoding_list,
                                      kUserSelectedEncodingsMaxLength);
  // Put 'cached encodings' (dynamic encoding list) after 'local dependent
  // encoding list' for check.
  std::vector<int> top_encoding_list(*locale_dependent_encoding_list);
  // UTF8 is always in our optimized encoding list.
  top_encoding_list.insert(top_encoding_list.begin(), IDC_ENCODING_UTF8);
  top_encoding_list.insert(top_encoding_list.end(),
                           selected_encoding_list.begin(),
                           selected_encoding_list.end());
  for (std::vector<int>::const_iterator it = top_encoding_list.begin();
       it != top_encoding_list.end(); ++it)
    if (*it == new_selected_encoding_id)
      return false;
  // Need to add the encoding id to recently selected encoding list.
  // Remove the last encoding in original list.
  if (selected_encoding_list.size() == kUserSelectedEncodingsMaxLength)
    selected_encoding_list.pop_back();
  // Insert new encoding to head of selected encoding list.
  *selected_encodings = encoding_name;
  // Generate the string for rest selected encoding list.
  for (std::vector<int>::const_iterator it = selected_encoding_list.begin();
       it != selected_encoding_list.end(); ++it) {
    selected_encodings->append(1, L',');
    selected_encodings->append(GetCanonicalEncodingNameByCommandId(*it));
  }
  return true;
}

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