Clean up forward declarations in Source/platform

Source/platform/mediastream/RTCStatsRequest.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 20 matching lines @@
 #ifndef RTCStatsRequest_h
 #define RTCStatsRequest_h
 
 #include "platform/heap/Handle.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class MediaStreamComponent;
-class MediaStreamDescriptor;
 class RTCStatsResponseBase;
 
 class RTCStatsRequest : public GarbageCollectedFinalized<RTCStatsRequest> {
 public:
     virtual ~RTCStatsRequest() { }
 
     virtual RTCStatsResponseBase* createResponse() = 0;
     virtual bool hasSelector() = 0;
     virtual MediaStreamComponent* component() = 0;
     virtual void requestSucceeded(RTCStatsResponseBase*) = 0;
 
     virtual void trace(Visitor*) { }
 
 protected:
     RTCStatsRequest() { }
 };
 
 } // namespace blink
 
 #endif // RTCStatsRequest_h