Eliminate OmniboxMetricsProvider listening to notification

ios/chrome/browser/omnibox/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 IOS_CHROME_BROWSER_OMNIBOX_OMNIBOX_EVENT_GLOBAL_TRACKER_H_
-#define IOS_CHROME_BROWSER_OMNIBOX_OMNIBOX_EVENT_GLOBAL_TRACKER_H_
-
-#include "base/callback_list.h"
-#include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
-
-template <typename T>
-struct DefaultSingletonTraits;
-
-struct OmniboxLog;
-
-// Omnibox code tracks events on a per-BrowserState basis, but there are
-// several clients who need to observe these events for all BrowserStates.
-// 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>;
-
-  OmniboxEventGlobalTracker();
-  ~OmniboxEventGlobalTracker();
-
-  base::CallbackList<void(OmniboxLog*)> on_url_opened_callback_list_;
-
-  DISALLOW_COPY_AND_ASSIGN(OmniboxEventGlobalTracker);
-};
-
-#endif  // IOS_CHROME_BROWSER_OMNIBOX_OMNIBOX_EVENT_GLOBAL_TRACKER_H_