Remove calls to MessageLoop::current() in extensions.

extensions/browser/file_reader.h

 // Copyright (c) 2011 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 EXTENSIONS_BROWSER_FILE_READER_H_
 #define EXTENSIONS_BROWSER_FILE_READER_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
 #include "extensions/common/extension_resource.h"
 
-namespace base {
-class MessageLoop;
-}
-
 // This file defines an interface for reading a file asynchronously on a
 // background thread.
 // Consider abstracting out a FilePathProvider (ExtensionResource) and moving
 // back to chrome/browser/net if other subsystems want to use it.
 class FileReader : public base::RefCountedThreadSafe<FileReader> {
  public:
   // Reports success or failure and the data of the file upon success.
   typedef base::Callback<void(bool, const std::string&)> Callback;
 
   FileReader(const extensions::ExtensionResource& resource,
              const Callback& callback);
 
   // Called to start reading the file on a background thread.  Upon completion,
   // the callback will be notified of the results.
   void Start();
 
  private:
   friend class base::RefCountedThreadSafe<FileReader>;
 
   virtual ~FileReader();
 
   void ReadFileOnBackgroundThread();
 
   extensions::ExtensionResource resource_;
   Callback callback_;
-  base::MessageLoop* origin_loop_;
+  const scoped_refptr<base::SingleThreadTaskRunner> origin_task_runner_;
 };
 
 #endif  // EXTENSIONS_BROWSER_FILE_READER_H_