Implement one-shot audio focus inside MediaSession

content/browser/media/session/media_session_impl.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_MEDIA_SESSION_MEDIA_SESSION_IMPL_H_
 #define CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_IMPL_H_
 
 #include <stddef.h>
 
 #include "base/callback_list.h"
@@ skipping 191 matching lines @@
 
   // Requests audio focus to the AudioFocusDelegate.
   // Returns whether the request was granted.
   CONTENT_EXPORT bool RequestSystemAudioFocus(
       AudioFocusManager::AudioFocusType audio_focus_type);
 
   // To be called after a call to AbandonAudioFocus() in order request the
   // delegate to abandon the audio focus.
   CONTENT_EXPORT void AbandonSystemAudioFocusIfNeeded();
 
-  // Notifies WebContents about the state change of the media session.
-  void UpdateWebContents();
+  // Notifies observers about the state change of the media session.
+  void DispatchStateChange();

[whywhat, 2016/11/03 14:32:17]

nit: you could call it NotifyObserversAboutStateChange or just
NotifyAboutStateChange or something to make the name match what's going on.
DispatchStateChange may sound like changing state of observers or something
else.

[Zhiqiang Zhang (Slow), 2016/11/04 14:10:54]

Done.

 
   // Internal method that should be used instead of setting audio_focus_state_.
   // It sets audio_focus_state_ and notifies observers about the state change.
   void SetAudioFocusState(State audio_focus_state);
 
   // Update the volume multiplier when ducking state changes.
   void UpdateVolumeMultiplier();
 
   // Get the volume multiplier, which depends on whether the media session is
   // ducking.
   double GetVolumeMultiplier() const;
 
   // Registers a MediaSessionImpl state change callback.
   CONTENT_EXPORT std::unique_ptr<base::CallbackList<void(State)>::Subscription>
   RegisterMediaSessionStateChangedCallbackForTest(
       const StateChangedCallback& cb);
 
   CONTENT_EXPORT bool AddPepperPlayer(MediaSessionPlayerObserver* observer,
                                       int player_id);
 
+  CONTENT_EXPORT bool AddOneShotPlayer(MediaSessionPlayerObserver* observer,
+                                       int player_id);
+
   std::unique_ptr<AudioFocusDelegate> delegate_;
   PlayersMap players_;

[whywhat, 2016/11/03 14:32:17]

nit: perhaps we should rename players_ into normal_players_ and have
AddNormalPlayer or something to highlight that pepper_players_ and
one_shot_players_ are not players_.

[Zhiqiang Zhang (Slow), 2016/11/04 14:10:54]

Done.

   PlayersMap pepper_players_;
+  PlayersMap one_shot_players_;
 
   State audio_focus_state_;
   MediaSession::SuspendType suspend_type_;
   AudioFocusManager::AudioFocusType audio_focus_type_;
 
   MediaSessionUmaHelper uma_helper_;
 
   // The ducking state of this media session. The initial value is |false|, and
   // is set to |true| after StartDucking(), and will be set to |false| after
   // StopDucking().
   bool is_ducking_;
 
   base::Optional<MediaMetadata> metadata_;
   base::CallbackList<void(State)> media_session_state_listeners_;
 
   base::ObserverList<MediaSessionObserver> observers_;
 
 #if defined(OS_ANDROID)
   std::unique_ptr<MediaSessionAndroid> session_android_;
 #endif  // defined(OS_ANDROID)
 
   DISALLOW_COPY_AND_ASSIGN(MediaSessionImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_IMPL_H_