Refactor the interface for the CrxDownloader to take a callback.

chrome/browser/component_updater/background_downloader_win.h

Index: chrome/browser/component_updater/background_downloader_win.h
diff --git a/chrome/browser/component_updater/background_downloader_win.h b/chrome/browser/component_updater/background_downloader_win.h
index 500bef8842e38ea79b95af3a05811444b1f600a9..c3ca4c46d511a42f4efa9fcd866ddde2f2dfd0a2 100644
--- a/chrome/browser/component_updater/background_downloader_win.h
+++ b/chrome/browser/component_updater/background_downloader_win.h
@@ -28,8 +28,7 @@ class BackgroundDownloader : public CrxDownloader {
   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: