Move Singleton and related structs to namespace base

components/omnibox/browser/omnibox_event_global_tracker.h

 // 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.
 
 #ifndef COMPONENTS_OMNIBOX_BROWSER_OMNIBOX_EVENT_GLOBAL_TRACKER_H_
 #define COMPONENTS_OMNIBOX_BROWSER_OMNIBOX_EVENT_GLOBAL_TRACKER_H_
 
 #include "base/callback_list.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}  // namespace base
 
 struct OmniboxLog;
 
 // Omnibox code tracks events on a per-user-context basis, but there are
 // several clients who need to observe these events for all user contexts
 // (e.g., all Profiles in the //chrome embedder).  This class serves as an
 // intermediary to bridge the gap: omnibox code calls the
 // OmniboxEventGlobalTracker singleton on an event of interest, and it then
 // forwards the event to its registered observers.
 class OmniboxEventGlobalTracker {
  public:
   typedef base::Callback<void(OmniboxLog*)> OnURLOpenedCallback;
 
   // Returns the instance of OmniboxEventGlobalTracker.
   static OmniboxEventGlobalTracker* GetInstance();
 
   // Registers |cb| to be invoked when user open an URL from the omnibox.
   scoped_ptr<base::CallbackList<void(OmniboxLog*)>::Subscription>
       RegisterCallback(const OnURLOpenedCallback& cb);
 
   // Called to notify all registered callbacks that an URL was opened from
   // the omnibox.
   void OnURLOpened(OmniboxLog* log);
 
  private:
-  friend struct DefaultSingletonTraits<OmniboxEventGlobalTracker>;
+  friend struct base::DefaultSingletonTraits<OmniboxEventGlobalTracker>;
 
   OmniboxEventGlobalTracker();
   ~OmniboxEventGlobalTracker();
 
   base::CallbackList<void(OmniboxLog*)> on_url_opened_callback_list_;
 
   DISALLOW_COPY_AND_ASSIGN(OmniboxEventGlobalTracker);
 };
 
 #endif  // COMPONENTS_OMNIBOX_BROWSER_OMNIBOX_EVENT_GLOBAL_TRACKER_H_