content: Cleanup class/struct forward declarations

content/public/browser/resource_context.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_RESOURCE_CONTEXT_H_
 #define CONTENT_PUBLIC_BROWSER_RESOURCE_CONTEXT_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "base/supports_user_data.h"
 #include "build/build_config.h"
 #include "content/common/content_export.h"
 
 class GURL;
 
 namespace net {
 class HostResolver;
 class KeygenHandler;
 class URLRequestContext;
 }
 
 namespace content {
 
-class AppCacheService;
-
 // ResourceContext contains the relevant context information required for
 // resource loading. It lives on the IO thread, although it is constructed on
 // the UI thread. It must be destructed on the IO thread.
 class CONTENT_EXPORT ResourceContext : public base::SupportsUserData {
  public:
   ResourceContext();
   ~ResourceContext() override;
   virtual net::HostResolver* GetHostResolver() = 0;
 
   // DEPRECATED: This is no longer a valid given isolated apps/sites and
@@ skipping 19 matching lines @@
   // 2) The embedder saves its salt across restarts.
   static std::string CreateRandomMediaDeviceIDSalt();
 
  private:
   const std::string media_device_id_salt_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RESOURCE_CONTEXT_H_