Don't reset BlockThirdPartyCookies to it's default value if the preference it managed.

chrome/browser/host_content_settings_map.cc

 // Copyright (c) 2010 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/host_content_settings_map.h"
 
 #include "base/command_line.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/browser_thread.h"
@@ skipping 778 matching lines @@
   }
 }
 
 void HostContentSettingsMap::ResetToDefaults() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   {
     AutoLock auto_lock(lock_);
     default_content_settings_ = ContentSettings();
     ForceDefaultsToBeExplicit();
+    // Clear all content settings map except the
+    // managed_default_content_settings.
     host_content_settings_.clear();
     off_the_record_settings_.clear();
-    block_third_party_cookies_ = false;
+    // Don't reset block third party cookies if they are managed.
+    if (!IsBlockThirdPartyCookiesManaged())
+      block_third_party_cookies_ = false;
     block_nonsandboxed_plugins_ = false;
   }
 
   if (!is_off_the_record_) {
     PrefService* prefs = profile_->GetPrefs();
     updating_preferences_ = true;
     prefs->ClearPref(prefs::kDefaultContentSettings);
     prefs->ClearPref(prefs::kContentSettingsPatterns);
+    // If the block third party cookies preference is managed we still must
+    // clear it in order to restore the default value for later when the
+    // preference is not managed anymore.
     prefs->ClearPref(prefs::kBlockThirdPartyCookies);
     prefs->ClearPref(prefs::kBlockNonsandboxedPlugins);
     updating_preferences_ = false;
     NotifyObservers(
         ContentSettingsDetails(Pattern(), CONTENT_SETTINGS_TYPE_DEFAULT, ""));
   }
 }
 
 void HostContentSettingsMap::Observe(NotificationType type,
                                      const NotificationSource& source,
@@ skipping 334 matching lines @@
   }
 
   for (size_t i = 0; i < move_items.size(); ++i) {
     Value* pattern_settings_dictionary = NULL;
     all_settings_dictionary->RemoveWithoutPathExpansion(
         move_items[i].first, &pattern_settings_dictionary);
     all_settings_dictionary->SetWithoutPathExpansion(
         move_items[i].second, pattern_settings_dictionary);
   }
 }