Implements N:M forwarding of OmniboxEditModel events on iOS.

ios/chrome/browser/omnibox/omnibox_edit_model_observer_relay.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_EDIT_MODEL_OBSERVER_RELAY_H_
+#define IOS_CHROME_BROWSER_OMNIBOX_OMNIBOX_EDIT_MODEL_OBSERVER_RELAY_H_
+
+#include "base/callback_list.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+
+template <typename T>
+struct DefaultSingletonTraits;
+
+struct OmniboxLog;
+
+// OmniboxEditModelObserverRelay does N:M matching between all OmniboxEditModel

[blundell, 2015/07/21 09:11:57]

How about something like:

"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."

[sdefresne, 2015/07/21 12:05:31]

Sounds better, done.

+// and all clients interested in the events independently of the source.
+class OmniboxEditModelObserverRelay {

[sdefresne, 2015/07/21 08:26:22]

I don't like this name, what do you think of "OmniboxEditModelEventDispatcher"
instead?

[blundell, 2015/07/21 09:11:57]

How about "OmniboxEventGlobalTracker"?

[sdefresne, 2015/07/21 12:05:31]

SGTM.

+ public:
+  typedef base::Callback<void(OmniboxLog*)> OnURLOpenedCallback;
+
+  // Returns the instance of OmniboxEditModelObserverRelay.
+  static OmniboxEditModelObserverRelay* GetInstance();
+
+  // Registers |cb| to be invoked when user open an URL from the omnibox.

[blundell, 2015/07/21 09:11:57]

nit: s/an URL/a URL

[sdefresne, 2015/07/21 12:05:31]

As discussed offline, both are correct and depends on how you pronounce "URL".

+  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<OmniboxEditModelObserverRelay>;
+
+  OmniboxEditModelObserverRelay();
+  ~OmniboxEditModelObserverRelay();
+
+  base::CallbackList<void(OmniboxLog*)> on_url_opened_callback_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(OmniboxEditModelObserverRelay);
+};
+
+#endif  // IOS_CHROME_BROWSER_OMNIBOX_OMNIBOX_EDIT_MODEL_OBSERVER_RELAY_H_