components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/prefs/browser_prefs.cc

Index: chrome/browser/prefs/browser_prefs.cc
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index fac503eae182efc64544c5143611bcbdb319f7b2..3bf1e5eb01ee78df6d024755abaf00c0a6d3aa01 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -268,7 +268,7 @@ void RegisterLocalState(PrefRegistrySimple* registry) {
 #endif
 }
 
-void RegisterUserPrefs(PrefRegistrySyncable* registry) {
+void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry) {
   // User prefs. Please keep this list alphabetized.
   AlternateErrorPageTabObserver::RegisterUserPrefs(registry);
   autofill::AutofillDialogControllerImpl::RegisterUserPrefs(registry);
@@ -371,8 +371,10 @@ void RegisterUserPrefs(PrefRegistrySyncable* registry) {
 
   // Prefs registered only for migration (clearing or moving to a new
   // key) go here.
-  registry->RegisterDictionaryPref(kBackupPref, new DictionaryValue(),
-                                   PrefRegistrySyncable::UNSYNCABLE_PREF);
+  registry->RegisterDictionaryPref(
+      kBackupPref,
+      new DictionaryValue(),
+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 void MigrateUserPrefs(Profile* profile) {