Move Singleton and related structs to namespace base

components/omnibox/browser/omnibox_event_global_tracker.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/omnibox/browser/omnibox_event_global_tracker.h"
 
 #include "base/memory/singleton.h"
 
 OmniboxEventGlobalTracker* OmniboxEventGlobalTracker::GetInstance() {
-  return Singleton<OmniboxEventGlobalTracker>::get();
+  return base::Singleton<OmniboxEventGlobalTracker>::get();
 }
 
 scoped_ptr<base::CallbackList<void(OmniboxLog*)>::Subscription>
 OmniboxEventGlobalTracker::RegisterCallback(const OnURLOpenedCallback& cb) {
   return on_url_opened_callback_list_.Add(cb);
 }
 
 void OmniboxEventGlobalTracker::OnURLOpened(OmniboxLog* log) {
   on_url_opened_callback_list_.Notify(log);
 }
 
 OmniboxEventGlobalTracker::OmniboxEventGlobalTracker() {}
 
 OmniboxEventGlobalTracker::~OmniboxEventGlobalTracker() {}