components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/chrome_content_browser_client.h

Index: chrome/browser/chrome_content_browser_client.h
diff --git a/chrome/browser/chrome_content_browser_client.h b/chrome/browser/chrome_content_browser_client.h
index 44ffbd541a246a77ec6554d1539c074dbee403c5..84703c1a501c0c7f6857ec19bfdc72256b7e7878 100644
--- a/chrome/browser/chrome_content_browser_client.h
+++ b/chrome/browser/chrome_content_browser_client.h
@@ -25,7 +25,9 @@ namespace extensions {
 class Extension;
 }
 
+namespace user_prefs {
 class PrefRegistrySyncable;
+}
 
 namespace chrome {
 
@@ -34,7 +36,7 @@ class ChromeContentBrowserClient : public content::ContentBrowserClient {
   ChromeContentBrowserClient();
   virtual ~ChromeContentBrowserClient();
 
-  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
+  static void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // Notification that the application locale has changed. This allows us to
   // update our I/O thread cache of this value.