Letting Flash join MediaSession (stack implementaion)

content/browser/media/session/audio_focus_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_AUDIO_FOCUS_MANAGER_H_
 #define CONTENT_BROWSER_MEDIA_SESSION_AUDIO_FOCUS_MANAGER_H_
 
+#include <list>
 #include <unordered_map>
 
 #include "base/memory/singleton.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/web_contents_observer.h"
 
 namespace content {
 
 class MediaSession;
 class WebContents;
@@ skipping 19 matching lines @@
   // TODO(mlamouri): in order to allow multiple MediaSession per WebContents, we
   // will have to keep track of MediaSession's. Though, we can easily keep track
   // of WebContents' life time right now but not MediaSession's.
   class AudioFocusEntry : public WebContentsObserver {
    public:
     AudioFocusEntry(WebContents* web_contents,
                     AudioFocusManager* audio_focus_manager,
                     AudioFocusType type);
 
     AudioFocusType type() const;
+    MediaSession* ToMediaSession() const;

[whywhat, 2016/09/13 00:16:17]

nit: This is a misleading name that is typically used when one wants to provide
a method to cast the base class to the derived class.

What if we hide the logic for interacting with MediaSession inside the audio
focus entry?
So the manager calls entry->IsActive() or something which calls
MediaSession::Get(web_contents())->IsActive();

if you do some check on the session before, you could combine it:

focus_entry->SuspendIfActive();

// replace the name with something that makes more sense for
AudioFocusManager/AudioFocusEntry.
void SuspendIfActive() {
  MediaSession* session = MediaSession::Get(web_contents());
  if (session->IsActive())
    session->Suspend();
}

This would decouple AudioFocusManager from the MediaSession class somewhat and
could be a good thing.

[Zhiqiang Zhang (Slow), 2016/09/22 12:30:33]

I think ultimately we should use MediaSession* in the stack. There's a lifetime
issue with MediaSession and WebContents (see comments above by Mounir), which
results in the current implementation.

I just renamed the method to `GetMediaSession()`

 
    private:
     // WebContentsObserver implementation.
     void WebContentsDestroyed() override;
 
     AudioFocusManager* audio_focus_manager_;  // Owns |this|.
     AudioFocusType type_;
 
     DISALLOW_COPY_AND_ASSIGN(AudioFocusEntry);
   };
 
   AudioFocusManager();
   ~AudioFocusManager();
 
   void OnWebContentsDestroyed(WebContents* web_contents);
 
-  // Internal usage of AbandonAudioFocus using WebContents.
-  void AbandonAudioFocusInternal(WebContents* web_contents);
-
-  // This method is meant to be called when a new session is of type
-  // GainTransientMayDuck. If it is the first one, other clients will be asked
-  // to duck.
-  void MaybeStartDucking() const;
-
-  // This method is meant to be called when a session is no longer of type
-  // GainTransientMayDuck. If it was the last one, other clients will be asked
-  // to no longer duck.
-  void MaybeStopDucking() const;
-
-  // Returns how many sessions require current audio focused session to duck.
-  int TransientMayDuckEntriesCount() const;
-
-  // Internal method to request audio focus of type AudioFocusType::Gain.
-  void RequestAudioFocusGain(WebContents* web_contents);
-
-  // Removes the entry associated with |web_contents| from the
-  // |transient_entries_| if there is one.
-  void MaybeRemoveTransientEntry(WebContents* web_contents);
-
-  // Removes the focused session if it is associated with |web_contents|.
   void MaybeRemoveFocusEntry(WebContents* web_contents);
 
-  std::unordered_map<WebContents*, std::unique_ptr<AudioFocusEntry>>
-      transient_entries_;
-  std::unique_ptr<AudioFocusEntry> focus_entry_;
+  std::list<std::unique_ptr<AudioFocusEntry>> audio_focus_stack_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_SESSION_AUDIO_FOCUS_MANAGER_H_