Revert of Revert of Propagate audible state from player to the containing tab"

content/browser/android/media_players_observer.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 CONTENT_BROWSER_ANDROID_MEDIA_PLAYERS_OBSERVER_H_
+#define CONTENT_BROWSER_ANDROID_MEDIA_PLAYERS_OBSERVER_H_
+
+#include <map>
+
+#include "base/macros.h"
+#include "content/browser/media/audio_state_provider.h"
+
+namespace content {
+
+class RenderFrameHost;
+
+// On Android the MediaPlayerAndroid objects report
+// the audible state to us.
+class MediaPlayersObserver : public AudioStateProvider {
+ public:
+  explicit MediaPlayersObserver(WebContents* web_contents);
+  ~MediaPlayersObserver() override;
+
+  bool IsAudioStateAvailable() const override;
+
+  // This audio state provider does not have a monitor,
+  // the method returns nullptr.
+  AudioStreamMonitor* audio_stream_monitor() override;
+
+  // These methods constitute the observer pattern, should
+  // be called when corresponding event happens. They will notify
+  // WebContents whenever its audible state as a whole changes.
+  void OnAudibleStateChanged(RenderFrameHost* rfh, int player_id,
+                             bool is_audible);
+  void RemovePlayer(RenderFrameHost* rfh, int player_id);
+  void RenderFrameDeleted(RenderFrameHost* rfh);
+
+ private:
+  void UpdateStatusAndNotify();
+
+  // Audible status per player ID and frame
+  typedef std::pair<RenderFrameHost*, int> Key;
+  typedef std::map<Key, bool> StatusMap;
+  StatusMap audio_status_map_;

[whywhat, 2015/04/24 12:35:47]

Drive-by: it seems instead of having a map<Key, bool> we could use a set<Key>
(the Key is only present when it's audible) and consider an empty set ==
non-audible WebContents. Has this been considered and if yes, why was it
dropped?

+
+  DISALLOW_COPY_AND_ASSIGN(MediaPlayersObserver);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ANDROID_MEDIA_PLAYERS_OBSERVER_H_