Revert of ios: Remove use of MessageLoopProxy and deprecated MessageLoop APIs

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 "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/message_loop/message_loop_proxy.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 {
 
 class ShellURLRequestContextGetter : public net::URLRequestContextGetter {
  public:
   ShellURLRequestContextGetter(
       const base::FilePath& base_path,
       const scoped_refptr<base::SingleThreadTaskRunner>& network_task_runner,
       const scoped_refptr<base::SingleThreadTaskRunner>& file_task_runner,
-      const scoped_refptr<base::SingleThreadTaskRunner>& cache_task_runner);
+      const scoped_refptr<base::MessageLoopProxy>& cache_task_runner);
 
   // net::URLRequestContextGetter implementation.
   net::URLRequestContext* GetURLRequestContext() override;
   scoped_refptr<base::SingleThreadTaskRunner> GetNetworkTaskRunner()
       const override;
 
  protected:
   ~ShellURLRequestContextGetter() override;
 
  private:
   base::FilePath base_path_;
   scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> network_task_runner_;
-  scoped_refptr<base::SingleThreadTaskRunner> cache_task_runner_;
+  scoped_refptr<base::MessageLoopProxy> cache_task_runner_;
   scoped_ptr<net::ProxyConfigService> proxy_config_service_;
   scoped_ptr<net::NetworkDelegate> network_delegate_;
   scoped_ptr<net::URLRequestContextStorage> storage_;
   scoped_ptr<net::URLRequestContext> url_request_context_;
   scoped_ptr<net::NetLog> net_log_;
   scoped_ptr<net::TransportSecurityPersister> transport_security_persister_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellURLRequestContextGetter);
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_SHELL_SHELL_URL_REQUEST_CONTEXT_GETTER_H_