Hook up RendererMediaSessionManager with browser side

third_party/WebKit/public/platform/modules/mediasession/WebMediaSession.h

 // Copyright 2015 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 WebMediaSession_h
 #define WebMediaSession_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/modules/mediasession/WebMediaSessionError.h"
 
 namespace blink {
 
 using WebMediaSessionActivateCallback = WebCallbacks<void, const WebMediaSessionError&>;
 using WebMediaSessionDeactivateCallback = WebCallbacks<void, void>;
 
 class WebMediaSession {
 public:
     virtual ~WebMediaSession() = default;
 
     virtual void activate(WebMediaSessionActivateCallback*) = 0;
     virtual void deactivate(WebMediaSessionDeactivateCallback*) = 0;
+
+    virtual bool hasPendingCallbacks() = 0;
 };
 
 } // namespace blink
 
 #endif // WebMediaSession_h