Revert of Letting Flash join MediaSession (stack implementaion)

content/browser/media/session/audio_focus_manager.h

Index: content/browser/media/session/audio_focus_manager.h
diff --git a/content/browser/media/session/audio_focus_manager.h b/content/browser/media/session/audio_focus_manager.h
index 9cbf13f06daac2de74f3edf743a510ee5d18ad1f..6844ae767c402324872af4f787b100f3722e0222 100644
--- a/content/browser/media/session/audio_focus_manager.h
+++ b/content/browser/media/session/audio_focus_manager.h
@@ -5,7 +5,6 @@
 #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"
@@ -15,6 +14,7 @@
 namespace content {
 
 class MediaSession;
+class WebContents;
 
 class CONTENT_EXPORT AudioFocusManager {
  public:
@@ -34,14 +34,61 @@
   friend struct base::DefaultSingletonTraits<AudioFocusManager>;
   friend class AudioFocusManagerTest;
 
+  // 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;
+
+   private:
+    // WebContentsObserver implementation.
+    void WebContentsDestroyed() override;
+
+    AudioFocusManager* audio_focus_manager_;  // Owns |this|.
+    AudioFocusType type_;
+
+    DISALLOW_COPY_AND_ASSIGN(AudioFocusEntry);
+  };
+
   AudioFocusManager();
   ~AudioFocusManager();
 
-  void MaybeRemoveFocusEntry(MediaSession* media_session);
+  void OnWebContentsDestroyed(WebContents* web_contents);
 
-  // Weak reference of managed MediaSessions. A MediaSession must abandon audio
-  // foucs before its destruction.
-  std::list<MediaSession*> audio_focus_stack_;
+  // 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_;
 };
 
 }  // namespace content