components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/ui/webui/extensions/extension_settings_handler.h

Index: chrome/browser/ui/webui/extensions/extension_settings_handler.h
diff --git a/chrome/browser/ui/webui/extensions/extension_settings_handler.h b/chrome/browser/ui/webui/extensions/extension_settings_handler.h
index bc198afc8b7b1814fd60d52f7283cb640005d177..49d9ec52d7e46652cf9ab711d219af63e1a01733 100644
--- a/chrome/browser/ui/webui/extensions/extension_settings_handler.h
+++ b/chrome/browser/ui/webui/extensions/extension_settings_handler.h
@@ -28,7 +28,6 @@
 #include "ui/shell_dialogs/select_file_dialog.h"
 
 class ExtensionService;
-class PrefRegistrySyncable;
 
 namespace base {
 class DictionaryValue;
@@ -46,6 +45,10 @@ class ExtensionHost;
 class ManagementPolicy;
 }
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 // Information about a page running in an extension, for example a popup bubble,
 // a background page, or a tab contents.
 struct ExtensionPage {
@@ -75,7 +78,7 @@ class ExtensionSettingsHandler
   ExtensionSettingsHandler();
   virtual ~ExtensionSettingsHandler();
 
-  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
+  static void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // Extension Detail JSON Struct for page. |pages| is injected for unit
   // testing.