Implements N:M forwarding of OmniboxEditModel events on iOS.

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_