components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/prefs/session_startup_pref.h

Index: chrome/browser/prefs/session_startup_pref.h
diff --git a/chrome/browser/prefs/session_startup_pref.h b/chrome/browser/prefs/session_startup_pref.h
index 9749cd2050c7eab5de71e2940355de1007c6f893..a31380fa82ebe5d329ea8545f2d1b95347f5fde6 100644
--- a/chrome/browser/prefs/session_startup_pref.h
+++ b/chrome/browser/prefs/session_startup_pref.h
@@ -10,9 +10,12 @@
 #include "googleurl/src/gurl.h"
 
 class PrefService;
-class PrefRegistrySyncable;
 class Profile;
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 // StartupPref specifies what should happen at startup for a specified profile.
 // StartupPref is stored in the preferences for a particular profile.
 struct SessionStartupPref {
@@ -41,7 +44,7 @@ struct SessionStartupPref {
   static const int kPrefValueURLs = 4;
   static const int kPrefValueNewTab = 5;
 
-  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
+  static void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // Returns the default value for |type|.
   static Type GetDefaultStartupType();