chrome: Cleanup class/struct forward declarations

chrome/browser/ui/cocoa/download/download_shelf_mac.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 CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_SHELF_MAC_H_
 #define CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_SHELF_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/compiler_specific.h"
 #include "chrome/browser/download/download_shelf.h"
 
-class DownloadItemModel;
-
 @class DownloadShelfController;
 
 // A class to bridge the chromium download shelf to mac gui. This is just a
 // wrapper class that forward everything to DownloadShelfController.
 
 class DownloadShelfMac : public DownloadShelf {
  public:
   DownloadShelfMac(Browser* browser, DownloadShelfController* controller);
 
   // DownloadShelf implementation.
   bool IsShowing() const override;
   bool IsClosing() const override;
   Browser* browser() const override;
 
  protected:
   void DoAddDownload(content::DownloadItem* download) override;
   void DoShow() override;
   void DoClose(CloseReason reason) override;
 
  private:
   // The browser that owns this shelf.
   Browser* browser_;
 
   DownloadShelfController* shelf_controller_;  // weak, owns us
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_DOWNLOAD_DOWNLOAD_SHELF_MAC_H_