Clean forward declaration in public

public/platform/WebPrescientNetworking.h

 /*
  * Copyright (C) 2013 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 WebPrescientNetworking_h
 #define WebPrescientNetworking_h
 
 #include "WebCommon.h"
 #include "WebString.h"
 
 namespace blink {
 
-class WebURL;
-
 class WebPrescientNetworking {
 public:
     virtual ~WebPrescientNetworking() { }
 
     // When a page navigation is speculated, DNS prefetch is triggered to hide
     // the host resolution latency.
     virtual void prefetchDNS(const WebString& hostname) { }
 };
 
 } // namespace blink
 
 #endif // WebPrescientNetworking_h