Link MediaSessionTabHelper with native MediaSession [CL is going to be split]

content/browser/media/session/media_session.h

Index: content/browser/media/session/media_session.h
diff --git a/content/browser/media/session/media_session.h b/content/browser/media/session/media_session.h
index 9239c7854a18b18326e2c2983451e49490922982..5641f0708be67c7164faf68e1dc89b5cbdde953d 100644
--- a/content/browser/media/session/media_session.h
+++ b/content/browser/media/session/media_session.h
@@ -7,9 +7,11 @@
 
 #include <stddef.h>
 
+#include "base/android/scoped_java_ref.h"
 #include "base/callback_list.h"
 #include "base/id_map.h"
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "base/optional.h"
 #include "content/browser/media/session/audio_focus_manager.h"
 #include "content/browser/media/session/media_session_uma_helper.h"
@@ -29,9 +31,14 @@ namespace content {
 class AudioFocusDelegate;
 class AudioFocusManagerTest;
 class MediaSessionPlayerObserver;
+class MediaSessionObserver;
 class MediaSessionStateObserver;
 class MediaSessionVisibilityBrowserTest;
 
+#if defined(OS_ANDROID)
+class MediaSessionAndroid;
+#endif  // defined(OS_ANDROID)
+
 // MediaSession manages the media session and audio focus for a given
 // WebContents. It is requesting the audio focus, pausing when requested by the
 // system and dropping it on demand.
@@ -71,6 +78,22 @@ class MediaSession : public WebContentsObserver,
 
   ~MediaSession() override;
 
+#if defined(OS_ANDROID)
+  static MediaSession* FromJavaMediaSession(
+      const base::android::JavaRef<jobject>& j_media_session);
+  MediaSessionAndroid* session_android() const {
+    return session_android_.get();
+  }
+#endif  // defined(OS_ANDROID)
+
+  // Add and remove an observer for MediaSession messages. Clients must remove
+  // the observer before they go away, or pass the observer ownership to
+  // MediaSession via PassObserverOwnership (then the observer will go away when
+  // the session is destroyed. AddObserver() can only be called in
+  // MediaSessionObserver constructor, and cannot be called explicitly.
+  void AddObserver(MediaSessionObserver* observer);
+  void RemoveObserver(MediaSessionObserver* observer);
+
   void SetMetadata(const base::Optional<MediaMetadata>& metadata);
   const base::Optional<MediaMetadata>& metadata() const { return metadata_; }
 
@@ -237,6 +260,13 @@ class MediaSession : public WebContentsObserver,
   base::Optional<MediaMetadata> metadata_;
   base::CallbackList<void(State)> media_session_state_listeners_;
 
+  // The list of observers notified when the MediaSession changes.
+  base::ObserverList<MediaSessionObserver> observers_;
+
+#if defined(OS_ANDROID)
+  std::unique_ptr<MediaSessionAndroid> session_android_;
+#endif  // defined(OS_ANDROID)
+
   DISALLOW_COPY_AND_ASSIGN(MediaSession);
 };