components: Move PrefRegistrySyncable into user_prefs namespace.

components/user_prefs/pref_registry_syncable.h

Index: components/user_prefs/pref_registry_syncable.h
diff --git a/components/user_prefs/pref_registry_syncable.h b/components/user_prefs/pref_registry_syncable.h
index 811209ba722f28142c5462b82efab54fa3f85369..9134d0b09d28a22934e3839039cb018e0b0f2a4f 100644
--- a/components/user_prefs/pref_registry_syncable.h
+++ b/components/user_prefs/pref_registry_syncable.h
@@ -18,6 +18,8 @@ class ListValue;
 class Value;
 }
 
+namespace user_prefs {
+
 // A PrefRegistry that forces users to choose whether each registered
 // preference is syncable or not.
 //
@@ -124,4 +126,6 @@ class USER_PREFS_EXPORT PrefRegistrySyncable : public PrefRegistry {
   DISALLOW_COPY_AND_ASSIGN(PrefRegistrySyncable);
 };
 
+}  // namespace user_prefs
+
 #endif  // COMPONENTS_USER_PREFS_PREF_REGISTRY_SYNCABLE_H_