chrome: Cleanup class/struct forward declarations

chrome/browser/ui/search/search_tab_helper_delegate.h

 // Copyright 2014 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_SEARCH_SEARCH_TAB_HELPER_DELEGATE_H_
 #define CHROME_BROWSER_UI_SEARCH_SEARCH_TAB_HELPER_DELEGATE_H_
 
 #include <set>
 #include <string>
 
 #include "ui/base/window_open_disposition.h"
 
 namespace content {
 class WebContents;
 }
 
-class GURL;
 class OmniboxView;
 
 // Objects implement this interface to get notified about changes in the
 // SearchTabHelper and to provide necessary functionality.
 class SearchTabHelperDelegate {
  public:
   // Invoked when the |web_contents| no longer supports Instant.
   virtual void OnWebContentsInstantSupportDisabled(
       const content::WebContents* web_contents);
 
   // Returns the OmniboxView or NULL if not available.
   virtual OmniboxView* GetOmniboxView();
 
   // Returns a set containing the canonical URLs of the currently open tabs.
   virtual std::set<std::string> GetOpenUrls();
 
  protected:
   virtual ~SearchTabHelperDelegate();
 };
 
 #endif  // CHROME_BROWSER_UI_SEARCH_SEARCH_TAB_HELPER_DELEGATE_H_