Refactor the interface for the CrxDownloader to take a callback.

chrome/browser/component_updater/background_downloader_win.h

 // Copyright 2013 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 CHROME_BROWSER_COMPONENT_UPDATER_BACKGROUND_DOWNLOADER_WIN_H_
 #define CHROME_BROWSER_COMPONENT_UPDATER_BACKGROUND_DOWNLOADER_WIN_H_
 
 #include "chrome/browser/component_updater/crx_downloader.h"
 
 #include <windows.h>
@@ skipping 10 matching lines @@
 // of this class and the CrxDownloader overrides are expected to be called
 // from the UI thread. The rest of the class code runs on the FILE thread in
 // a single threaded apartment. Instances of this class are created and
 // destroyed in the UI thread. See the implementation of the class destructor
 // for details regarding the clean up of resources acquired in this class.
 class BackgroundDownloader : public CrxDownloader {
  protected:
   friend class CrxDownloader;
   BackgroundDownloader(scoped_ptr<CrxDownloader> successor,
                        net::URLRequestContextGetter* context_getter,
-                       scoped_refptr<base::SequencedTaskRunner> task_runner,
-                       const DownloadCallback& download_callback);
+                       scoped_refptr<base::SequencedTaskRunner> task_runner);
   virtual ~BackgroundDownloader();
 
  private:
   // Overrides for CrxDownloader.
   virtual void DoStartDownload(const GURL& url) OVERRIDE;
 
   // Called asynchronously on the FILE thread at different stages during
   // the download. |OnDownloading| can be called multiple times.
   // |EndDownload| switches the execution flow from the FILE to the UI thread.
   // Accessing any data members of this object on the FILE thread after
@@ skipping 45 matching lines @@
 
   bool is_completed_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundDownloader);
 };
 
 }  // namespace component_updater
 
 #endif  // CHROME_BROWSER_COMPONENT_UPDATER_BACKGROUND_DOWNLOADER_WIN_H_