content: Cleanup class/struct forward declarations

content/public/browser/web_drag_dest_delegate.h

 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_WEB_DRAG_DEST_DELEGATE_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_DRAG_DEST_DELEGATE_H_
 
 #include "base/strings/string16.h"
 
-class GURL;
-
 namespace ui {
 class OSExchangeData;
 }
 
 namespace content {
 class WebContents;
-struct DropData;
 
 // An optional delegate that listens for drags of bookmark data.
 class WebDragDestDelegate {
  public:
   // Announces that a drag has started. It's valid that a drag starts, along
   // with over/enter/leave/drop notifications without receiving any bookmark
   // data.
   virtual void DragInitialize(WebContents* contents) = 0;
 
   // Notifications of drag progression.
   virtual void OnDragOver() = 0;
   virtual void OnDragEnter() = 0;
   virtual void OnDrop() = 0;
   // This should also clear any state kept about this drag.
   virtual void OnDragLeave() = 0;
 
 #if defined(USE_AURA)
   // Called at the start of every drag to supply the data associated with the
   // drag.
   virtual void OnReceiveDragData(const ui::OSExchangeData& data) = 0;
 #endif  // USE_AURA
 
   virtual ~WebDragDestDelegate() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_DRAG_DEST_DELEGATE_H_