extensions: Cleanup class/struct fwd declarations

extensions/shell/app/shell_main_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 EXTENSIONS_SHELL_APP_SHELL_MAIN_DELEGATE_H_
 #define EXTENSIONS_SHELL_APP_SHELL_MAIN_DELEGATE_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
 #include "build/build_config.h"
 #include "content/public/app/content_main_delegate.h"
 
 namespace content {
-class BrowserContext;
 class ContentBrowserClient;
 class ContentClient;
 class ContentRendererClient;
 }
 
 namespace extensions {
-class ShellBrowserMainDelegate;
 
 class ShellMainDelegate : public content::ContentMainDelegate {
  public:
   ShellMainDelegate();
   ~ShellMainDelegate() override;
 
   // ContentMainDelegate implementation:
   bool BasicStartupComplete(int* exit_code) override;
   void PreSandboxStartup() override;
   content::ContentBrowserClient* CreateContentBrowserClient() override;
@@ skipping 23 matching lines @@
   std::unique_ptr<content::ContentBrowserClient> browser_client_;
   std::unique_ptr<content::ContentRendererClient> renderer_client_;
   std::unique_ptr<content::ContentUtilityClient> utility_client_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellMainDelegate);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_APP_SHELL_MAIN_DELEGATE_H_