Remove the migration code from content_settings::DefaultProvider.

components/content_settings/core/common/pref_names.cc

 // Copyright 2014 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 "components/content_settings/core/common/pref_names.h"
 
 namespace prefs {
 
 // Boolean that is true if we should unconditionally block third-party cookies,
 // regardless of other content settings.
 const char kBlockThirdPartyCookies[] = "profile.block_third_party_cookies";
 
 // Version of the pattern format used to define content settings.
 const char kContentSettingsVersion[] = "profile.content_settings.pref_version";
 
 // Patterns for mapping origins to origin related settings. Default settings
 // will be applied to origins that don't match any of the patterns. The pattern
 // format used is defined by kContentSettingsVersion.
 const char kContentSettingsPatternPairs[] =
     "profile.content_settings.pattern_pairs";
 
 // Integer that specifies the index of the tab the user was on when they
 // last visited the content settings window.
 const char kContentSettingsWindowLastTabIndex[] =
     "content_settings_window.last_tab_index";
 
-// Dictionary of content settings applied to all hosts by default.
-// TODO(msramek): Deprecated. Use the individual preferences below.
-const char kDefaultContentSettings[] = "profile.default_content_settings";
-
-// Whether |kDefaultContentSettings| has already been migrated to
-// |kDefault<type>Setting| prefs.
-const char kMigratedDefaultContentSettings[] =
-    "profile.migrated_default_content_settings";

[battre, 2015/07/27 08:32:36]

I think there is traditionally one more step:

Move this out of the public .../pref_names.{cc,h} files into
content_settings_default_provider.cc as kObsolete...; then add a function
DiscardObsoletePreferences that is called from
DefaultProvider::RegisterProfilePrefs and deletes the entries from the
preferences file so that it does not collect unused junk over time.

[msramek, 2015/07/27 09:13:27]

Done. But it cannot be called from static RegisterProfilePrefs, as it refers to
non-static member PrefService.

-
 // Preferences storing the default values for individual content settings.
 const char kDefaultCookiesSetting[] =
     "profile.default_content_setting_values.cookies";
 const char kDefaultImagesSetting[] =
     "profile.default_content_setting_values.images";
 const char kDefaultJavaScriptSetting[] =
     "profile.default_content_setting_values.javascript";
 const char kDefaultPluginsSetting[] =
     "profile.default_content_setting_values.plugins";
 const char kDefaultPopupsSetting[] =
@@ skipping 157 matching lines @@
 const char kManagedPopupsBlockedForUrls[] =
     "profile.managed_popups_blocked_for_urls";
 const char kManagedNotificationsAllowedForUrls[] =
     "profile.managed_notifications_allowed_for_urls";
 const char kManagedNotificationsBlockedForUrls[] =
     "profile.managed_notifications_blocked_for_urls";
 const char kManagedAutoSelectCertificateForUrls[] =
     "profile.managed_auto_select_certificate_for_urls";
 
 }  // namespace prefs