function loadDriveApi() {
    if (!wtf.io.drive.downloadFileLoadResult_) {
      wtf.io.drive.downloadFileLoadResult_ = new goog.result.SimpleResult();
      gapi.client.load('drive', 'v2', function() {
        wtf.io.drive.downloadFileLoadResult_.setValue(true);
      });
    }
    goog.result.wait(wtf.io.drive.downloadFileLoadResult_, download);
  }
Begins downloading a file from Drive.
The async result from this is an XHR that is about to start downloading. Just
call {@code send()} on it to kick off the process. This allows you to listen
for any progress events you require.
@param {wtf.io.drive.DriveFile} driveFile Drive file result from a
    call to {@see wtf.io.drive#queryFile}.
@return {!goog.result.Result} Async result. The value will be an XHR object.