Clean forward declaration in public

public/platform/WebDragData.h

 /*
  * Copyright (C) 2009 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 21 matching lines @@
 #define WebDragData_h
 
 #include "WebCommon.h"
 #include "WebData.h"
 #include "WebString.h"
 #include "WebURL.h"
 
 namespace blink {
 
 class DataObject;
-class WebDragDataPrivate;
 template <typename T> class WebVector;
 
 // Holds data that may be exchanged through a drag-n-drop operation. It is
 // inexpensive to copy a WebDragData object.
 class WebDragData {
 public:
     struct Item {
         enum StorageType {
             // String data with an associated MIME type. Depending on the MIME type, there may be
             // optional metadata attributes as well.
@@ skipping 61 matching lines @@
 #endif
 
 private:
     void ensureMutable();
     WebPrivatePtr<DataObject> m_private;
 };
 
 } // namespace blink
 
 #endif