ios: Cleanup class/struct forward declarations

ios/web/shell/shell_url_request_context_getter.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 IOS_WEB_SHELL_SHELL_URL_REQUEST_CONTEXT_GETTER_H_
 #define IOS_WEB_SHELL_SHELL_URL_REQUEST_CONTEXT_GETTER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "net/url_request/url_request_context_getter.h"
 
 namespace net {
-class HostResolver;
-class MappedHostResolver;
 class NetworkDelegate;
 class NetLog;
 class ProxyConfigService;
 class TransportSecurityPersister;
 class URLRequestContext;
 class URLRequestContextStorage;
 }
 
 namespace web {
 
@@ skipping 25 matching lines @@
   std::unique_ptr<net::NetLog> net_log_;
   std::unique_ptr<net::TransportSecurityPersister>
       transport_security_persister_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellURLRequestContextGetter);
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_SHELL_SHELL_URL_REQUEST_CONTEXT_GETTER_H_