drive: Fix DriveFileStreamReader to run cancel closure on the right thread

BUG=None

Review URL: https://codereview.chromium.org/98833003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238399 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/drive/drive_file_stream_reader.cc

@@ -360,7 +360,7 @@ void DriveFileStreamReader::InitializeAfterGetFileContentInitialized(
     // needed and and invalidate weak pointers so that we won't
     // receive unwanted callbacks.
     if (!ui_cancel_download_closure.is_null())
-      ui_cancel_download_closure.Run();
+      RunTaskOnUIThread(ui_cancel_download_closure);
     weak_ptr_factory_.InvalidateWeakPtrs();
     callback.Run(
         net::ERR_REQUEST_RANGE_NOT_SATISFIABLE, scoped_ptr<ResourceEntry>());