components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/prefs/browser_prefs.h

Index: chrome/browser/prefs/browser_prefs.h
diff --git a/chrome/browser/prefs/browser_prefs.h b/chrome/browser/prefs/browser_prefs.h
index 0b3aae169ef33b34dc8738caa6002acdab2c44d5..ecd97360ae58213f85adfaaeffa6055289a95d17 100644
--- a/chrome/browser/prefs/browser_prefs.h
+++ b/chrome/browser/prefs/browser_prefs.h
@@ -6,17 +6,20 @@
 #define CHROME_BROWSER_PREFS_BROWSER_PREFS_H_
 
 class PrefRegistrySimple;
-class PrefRegistrySyncable;
 class PrefService;
 class Profile;
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 namespace chrome {
 
 // Register all prefs that will be used via the local state PrefService.
 void RegisterLocalState(PrefRegistrySimple* registry);
 
 // Register all prefs that will be used via a PrefService attached to a Profile.
-void RegisterUserPrefs(PrefRegistrySyncable* registry);
+void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
 // Migrates prefs from |local_state| to |profile|'s pref store.
 void MigrateBrowserPrefs(Profile* profile, PrefService* local_state);