Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/session/media_session_controllers_manager.h

+// Copyright 2016 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 CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_CONTROLLERS_MANAGER_H_
+#define CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_CONTROLLERS_MANAGER_H_
+
+#include <map>
+#include <utility>
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+
+namespace content {
+
+class MediaSessionController;
+class MediaWebContentsObserver;
+class RenderFrameHost;
+
+using MediaPlayerId = std::pair<RenderFrameHost*, int>;

[DaleCurtis, 2016/02/26 03:22:50]

Why not include web_contents_observer.h to get this. Or put it somewhere else
that WCO can include?

[mlamouri (slow - plz ping), 2016/02/26 12:26:17]

I don't really like the idea of including a file like that for a type def but I
guess it's probably cleaner. I've added a comment saying that it's needed for
MediaPlayerId.

+
+// MediaSessionControllersManager is a delegate of MediaWebContentsObserver that
+// handles MediaSessionController instances.
+class MediaSessionControllersManager {

[DaleCurtis, 2016/02/26 03:22:50]

You'll want CONTENT_EXPORT if you're planning to write a unittest for this.

[mlamouri (slow - plz ping), 2016/02/26 12:26:17]

There are no tests for this. I don't think adding yet more stuff to this CL will
do any good. Opened a bug to add unit tests for M51: https://crbug.com/590183

+ public:
+  explicit MediaSessionControllersManager(
+      MediaWebContentsObserver* media_web_contents_observer);
+  ~MediaSessionControllersManager();
+
+  // Clear all the MediaSessionController associated with the given
+  // |render_frame_host|.
+  void Clear(RenderFrameHost* render_frame_host);
+
+  // Called before a player starts playing. It will be added to the media
+  // session and will have a controller associated with it.
+  // Returns whether the player was added to the session and can start playing.
+  bool RequestPlay(const MediaPlayerId& id, bool has_audio, bool is_remote,
+                   base::TimeDelta duration);
+
+  // Called when the given player |id| has paused.
+  void OnPause(const MediaPlayerId& id);
+
+  // Called when the given player |id| has ended.
+  void OnEnd(const MediaPlayerId& id);
+
+ private:
+  static bool IsDefaultMediaSessionEnabled();

[DaleCurtis, 2016/02/26 03:22:50]

Keep as a .cc local method? 

[mlamouri (slow - plz ping), 2016/02/26 12:26:17]

Done.

+
+  // Weak pointer because |this| is owned by |media_web_contents_observer_|.
+  MediaWebContentsObserver* const media_web_contents_observer_;
+
+  using ControllersMap =
+      std::map<MediaPlayerId, scoped_ptr<MediaSessionController>>;
+  ControllersMap controllers_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSessionControllersManager);
+};
+
+}  // namespace content
+
+#endif // CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_CONTROLLERS_MANAGER_H_