blink: Cleanup core class forward declarations

third_party/WebKit/Source/core/observer/ResizeObserverCallback.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 ResizeObserverCallback_h
 #define ResizeObserverCallback_h
 
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
-class ExecutionContext;
 class ResizeObserver;
 class ResizeObserverEntry;
 
 class ResizeObserverCallback
     : public GarbageCollectedFinalized<ResizeObserverCallback> {
  public:
   virtual ~ResizeObserverCallback() {}
   virtual void handleEvent(
       const HeapVector<Member<ResizeObserverEntry>>& entries,
       ResizeObserver*) = 0;
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 };
 
 }  // namespace blink
 
 #endif  // ResizeObserverCallback_h