components: Move PrefRegistrySyncable into user_prefs namespace.

components/user_prefs/pref_registry_syncable.cc

Index: components/user_prefs/pref_registry_syncable.cc
diff --git a/components/user_prefs/pref_registry_syncable.cc b/components/user_prefs/pref_registry_syncable.cc
index 9a3a76d3a80cb83b48ba6e04bd6ce29fada041ff..4ffd6393ba4e40fd665f0dc1a5b5dea6d30e8eac 100644
--- a/components/user_prefs/pref_registry_syncable.cc
+++ b/components/user_prefs/pref_registry_syncable.cc
@@ -10,6 +10,8 @@
 #include "base/values.h"
 #include "ui/base/l10n/l10n_util.h"
 
+namespace user_prefs {
+
 namespace {
 
 // A helper function for RegisterLocalized*Pref that creates a Value*
@@ -219,3 +221,5 @@ scoped_refptr<PrefRegistrySyncable> PrefRegistrySyncable::ForkForIncognito() {
   registry->defaults_ = defaults_;
   return registry;
 }
+
+}  // namespace user_prefs