URLFetcher uses a TaskRunner instead of a message loop.

net/url_request/url_fetcher.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 NET_URL_REQUEST_URL_FETCHER_H_
 #define NET_URL_REQUEST_URL_FETCHER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "base/platform_file.h"
 #include "base/supports_user_data.h"
+#include "base/task_runner.h"
 #include "net/base/net_export.h"
 
 class FilePath;
 class GURL;
 
 namespace base {
 class MessageLoopProxy;
 class TimeDelta;
 }
 
@@ skipping 162 matching lines @@
 
   virtual void SetMaxRetries(int max_retries) = 0;
   virtual int GetMaxRetries() const = 0;
 
   // Returns the back-off delay before the request will be retried,
   // when a 5xx response was received.
   virtual base::TimeDelta GetBackoffDelay() const = 0;
 
   // By default, the response is saved in a string. Call this method to save the
   // response to a file instead. Must be called before Start().
-  // |file_message_loop_proxy| will be used for all file operations.
+  // |file_task_runner| will be used for all file operations.
   // To save to a temporary file, use SaveResponseToTemporaryFile().
   // The created file is removed when the URLFetcher is deleted unless you
   // take ownership by calling GetResponseAsFilePath().
   virtual void SaveResponseToFileAtPath(
       const FilePath& file_path,
-      scoped_refptr<base::MessageLoopProxy> file_message_loop_proxy) = 0;
+      scoped_refptr<base::TaskRunner> file_task_runner) = 0;
 
   // By default, the response is saved in a string. Call this method to save the
   // response to a temporary file instead. Must be called before Start().
-  // |file_message_loop_proxy| will be used for all file operations.
+  // |file_task_runner| will be used for all file operations.
   // The created file is removed when the URLFetcher is deleted unless you
   // take ownership by calling GetResponseAsFilePath().
   virtual void SaveResponseToTemporaryFile(
-      scoped_refptr<base::MessageLoopProxy> file_message_loop_proxy) = 0;
+      scoped_refptr<base::TaskRunner> file_task_runner) = 0;
 
   // Retrieve the response headers from the request.  Must only be called after
   // the OnURLFetchComplete callback has run.
   virtual HttpResponseHeaders* GetResponseHeaders() const = 0;
 
   // Retrieve the remote socket address from the request.  Must only
   // be called after the OnURLFetchComplete callback has run and if
   // the request has not failed.
   virtual HostPortPair GetSocketAddress() const = 0;
 
@@ skipping 40 matching lines @@
   // true, caller takes responsibility for the file, and it will not
   // be removed once the URLFetcher is destroyed.  User should not take
   // ownership more than once, or call this method after taking ownership.
   virtual bool GetResponseAsFilePath(bool take_ownership,
                                      FilePath* out_response_path) const = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_FETCHER_H_