components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/ui/browser_ui_prefs.h

Index: chrome/browser/ui/browser_ui_prefs.h
diff --git a/chrome/browser/ui/browser_ui_prefs.h b/chrome/browser/ui/browser_ui_prefs.h
index 135a76cdbd75548faf4646793fddad22f9583419..9b137ccd60f89cba32b5e3008e053b1880d8fe33 100644
--- a/chrome/browser/ui/browser_ui_prefs.h
+++ b/chrome/browser/ui/browser_ui_prefs.h
@@ -8,13 +8,16 @@
 #include <string>
 
 class PrefRegistrySimple;
-class PrefRegistrySyncable;
 class Profile;
 
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
 namespace chrome {
 
 void RegisterBrowserPrefs(PrefRegistrySimple* registry);
-void RegisterBrowserUserPrefs(PrefRegistrySyncable* registry);
+void RegisterBrowserUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
 // Create a preference dictionary for the provided application name, in the
 // given user profile. This is done only once per application name / per