ash: Cleanup class/struct forward declarations

ash/shell/content/client/shell_content_browser_client.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 ASH_SHELL_CONTENT_CLIENT_SHELL_CONTENT_BROWSER_CLIENT_H_
 #define ASH_SHELL_CONTENT_CLIENT_SHELL_CONTENT_BROWSER_CLIENT_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "content/public/browser/content_browser_client.h"
 
 namespace content {
-class ShellBrowserContext;
 class ShellBrowserMainParts;
-class ShellResourceDispatcherHostDelegate;
 }
 
 namespace ash {
 namespace shell {
 
 class ShellBrowserMainParts;
 
 class ShellContentBrowserClient : public content::ContentBrowserClient {
  public:
   ShellContentBrowserClient();
   ~ShellContentBrowserClient() override;
 
   // Overridden from content::ContentBrowserClient:
   content::BrowserMainParts* CreateBrowserMainParts(
       const content::MainFunctionParams& parameters) override;
 
  private:
   ShellBrowserMainParts* shell_browser_main_parts_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellContentBrowserClient);
 };
 
 }  // namespace shell
 }  // namespace ash
 
 #endif  // ASH_SHELL_CONTENT_CLIENT_SHELL_CONTENT_BROWSER_CLIENT_H_