Make MediaSession per frame as an attribute of Navigator

third_party/WebKit/Source/modules/mediasession/NavigatorMediaSession.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 NavigatorMediaSession_h
+#define NavigatorMediaSession_h
+
+#include "core/frame/Navigator.h"
+#include "modules/mediasession/MediaSession.h"
+#include "platform/Supplementable.h"
+
+namespace blink {
+
+class Navigator;
+
+// Provides MediaSession as a supplement of Navigator as an attribute.
+class NavigatorMediaSession final
+    : public GarbageCollected<NavigatorMediaSession>,
+      public Supplement<Navigator> {
+  USING_GARBAGE_COLLECTED_MIXIN(NavigatorMediaSession);
+
+ public:
+  static NavigatorMediaSession& from(Navigator&);
+  static MediaSession* mediaSession(Navigator&);
+
+  DECLARE_TRACE();
+
+ private:
+  NavigatorMediaSession(Navigator&);
+  static const char* supplementName();
+
+  // The MediaSession instance of this Navigator.
+  Member<MediaSession> m_session;
+};
+
+}  // namespace blink
+
+#endif  // NavigatorMediaSession_h