Decouple MediaSession messages from WebContents (full patch)

content/public/browser/media_session_observer.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_PUBLIC_BROWSER_MEDIA_SESSION_OBSERVER_H_
+#define CONTENT_PUBLIC_BROWSER_MEDIA_SESSION_OBSERVER_H_
+
+#include "base/macros.h"
+#include "base/optional.h"
+#include "content/common/content_export.h"
+#include "content/public/common/media_metadata.h"
+
+namespace content {
+
+class MediaSession;
+class MediaSessionImpl;
+
+// The observer for observing MediaSession events.
+class CONTENT_EXPORT MediaSessionObserver {
+ public:
+  // Gets the observed MediaSession. Will return null when the session is
+  // destroyed.
+  MediaSession* media_session() const;
+
+  // Called when the observed MediaSession is being destroyed. Give subclass a
+  // chance to clean up. media_session() will return nullptr after this method
+  // is called.
+  virtual void MediaSessionDestroyed() {}
+
+  // Called when the observed MediaSession has changed its state.
+  virtual void MediaSessionStateChanged(bool is_controllable,
+                                        bool is_suspended) {}
+
+  // Called when the observed MediaSession has changed metadata.
+  virtual void MediaSessionMetadataChanged(
+      const base::Optional<MediaMetadata>& metadata) {}
+
+ protected:
+  // Create a MediaSessionObserver and start observing a session.
+  MediaSessionObserver(MediaSession* media_session);
+  // Destruct a MediaSessionObserver and remove it from the session if it's
+  // still observing.
+  virtual ~MediaSessionObserver();
+
+ private:
+  friend class MediaSessionImpl;
+
+  void StopObserving();
+
+  // Weak pointer to MediaSession
+  MediaSessionImpl* media_session_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaSessionObserver);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_MEDIA_SESSION_OBSERVER_H_