URLFetcher uses a TaskRunner instead of a message loop.

net/url_request/url_fetcher_impl.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.
 
 // This file contains URLFetcher, a wrapper around URLRequest that handles
 // low-level details like thread safety, ref counting, and incremental buffer
 // reading.  This is useful for callers who simply want to get the data from a
 // URL and don't care about all the nitty-gritty details.
 //
 // NOTE(willchan): Only one "IO" thread is supported for URLFetcher.  This is a
@@ skipping 45 matching lines @@
   virtual void SetURLRequestUserData(
       const void* key,
       const CreateDataCallback& create_data_callback) OVERRIDE;
   virtual void SetStopOnRedirect(bool stop_on_redirect) OVERRIDE;
   virtual void SetAutomaticallyRetryOn5xx(bool retry) OVERRIDE;
   virtual void SetMaxRetries(int max_retries) OVERRIDE;
   virtual int GetMaxRetries() const OVERRIDE;
   virtual base::TimeDelta GetBackoffDelay() const OVERRIDE;
   virtual void SaveResponseToFileAtPath(
       const FilePath& file_path,
-      scoped_refptr<base::MessageLoopProxy> file_message_loop_proxy) OVERRIDE;
+      scoped_refptr<base::TaskRunner> file_task_runner) OVERRIDE;
   virtual void SaveResponseToTemporaryFile(
-      scoped_refptr<base::MessageLoopProxy> file_message_loop_proxy) OVERRIDE;
+      scoped_refptr<base::TaskRunner> file_task_runner) OVERRIDE;
   virtual HttpResponseHeaders* GetResponseHeaders() const OVERRIDE;
   virtual HostPortPair GetSocketAddress() const OVERRIDE;
   virtual bool WasFetchedViaProxy() const OVERRIDE;
   virtual void Start() OVERRIDE;
   virtual const GURL& GetOriginalURL() const OVERRIDE;
   virtual const GURL& GetURL() const OVERRIDE;
   virtual const URLRequestStatus& GetStatus() const OVERRIDE;
   virtual int GetResponseCode() const OVERRIDE;
   virtual const ResponseCookies& GetCookies() const OVERRIDE;
   virtual bool FileErrorOccurred(
@@ skipping 33 matching lines @@
   static int GetNumFetcherCores();
 
   const scoped_refptr<URLFetcherCore> core_;
 
   DISALLOW_COPY_AND_ASSIGN(URLFetcherImpl);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_FETCHER_IMPL_H_