Clean up forward declarations in Source/core/loader

Source/core/loader/PrerendererClient.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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  *
  */
 
 #ifndef PrerendererClient_h
 #define PrerendererClient_h
 
 #include "platform/Supplementable.h"
 
 namespace blink {
 
-class Document;
 class Page;
 class Prerender;
 
 class PrerendererClient : public WillBeHeapSupplement<Page> {
 public:
     virtual void willAddPrerender(Prerender*) = 0;
 
     static const char* supplementName();
     static PrerendererClient* from(Page*);
 
 protected:
     PrerendererClient() { }
 };
 
 void providePrerendererClientTo(Page&, PrerendererClient*);
 
 } // namespace blink
 
 #endif // PrerendererClient_h