Implement MediaSession on top of the WebMediaPlayerDelegate.

content/browser/media/android/media_session_controller.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_ANDROID_MEDIA_SESSION_CONTROLLER_H_
+#define CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_CONTROLLER_H_
+
+#include "base/time/time.h"
+#include "content/browser/media/android/media_session_observer.h"
+#include "content/browser/media/media_web_contents_observer.h"

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

nit: I think you should be able to fwd clare this.

[DaleCurtis, 2016/01/23 02:10:59]

Done, but requires including WebContentsObserver now for the MediaPlayerId.

+#include "content/common/content_export.h"
+
+namespace content {
+
+// Helper class for controlling a single player's MediaSession instance.  Sends
+// browser side MediaSession commands back to a player hosted in the renderer
+// process.
+class CONTENT_EXPORT MediaSessionController : public MediaSessionObserver {
+ public:
+  MediaSessionController(const WebContentsObserver::MediaPlayerId& id,
+                         MediaWebContentsObserver* media_web_contents_observer);
+  ~MediaSessionController() override;
+
+  // Minimum duration of content for a MediaSession instance to be created.
+  enum { kMinimumDurationForContentSecs = 5 };
+
+  // Clients must call this after construction and destroy the controller if it
+  // returns false.
+  bool Initialize(bool has_audio, bool is_remote, base::TimeDelta duration);
+
+  // Must be called when a pause occurs on the renderer side media player; keeps
+  // the MediaSession instance in sync with renderer side behavior.
+  void PausePlayback();

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

nit: why not `OnPausePlayback()`. It sounds like this method will actually pause
the playback.

[DaleCurtis, 2016/01/23 02:10:59]

Went with OnPlaybackPaused() since this is reflecting an event that already
happened in the renderer.

+
+  // MediaSessionObserver implementation.
+  void OnSuspend(int player_id) override;
+  void OnResume(int player_id) override;
+  void OnSetVolumeMultiplier(int player_id, double volume_multiplier) override;
+
+  // TODO(dalecurtis): Remove once WMPA is removed and there are no inaccurate
+  // setting reports.
+  bool has_audio() { return has_audio_; }

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

nit: `const`

[DaleCurtis, 2016/01/23 02:10:59]

Done.

+
+  int get_player_id_for_testing() { return player_id_; }

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

nit: `const`

[DaleCurtis, 2016/01/23 02:10:59]

Done.

+
+ private:
+  const WebContentsObserver::MediaPlayerId id_;
+  MediaWebContentsObserver* const media_web_contents_observer_;

[mlamouri (slow - plz ping), 2016/01/22 16:58:31]

Can you explain the ownership of this in a comment. I guess here just say that
`media_web_contents_observer_` owns this object.

[DaleCurtis, 2016/01/23 02:10:59]

Done.

+  int player_id_ = 0;
+  bool initialized_ = false;
+  bool has_audio_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSessionController);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_CONTROLLER_H_