message: feat(GUI): add drive quantity to flash analytics
  We add a field `driveCount` to the flash analytics events in the image
  writer.
  Change-Type: patch
diff: @@ -160,6 +160,7 @@ exports.performWrite = (image, drives, onProgress) => {
  const analyticsData = {
  image,
  drives,
  + driveCount: drives.length,
  uuid: flashState.getFlashUuid(),
  unmountOnSuccess: settings.get('unmountOnSuccess'),
  validateWriteOnSuccess: settings.get('validateWriteOnSuccess')
  @@ -299,6 +300,7 @@ exports.flash = (image, drives) => {
  const analyticsData = {
  image,
  drives,
  + driveCount: drives.length,
  uuid: flashState.getFlashUuid(),
  unmountOnSuccess: settings.get('unmountOnSuccess'),
  validateWriteOnSuccess: settings.get('validateWriteOnSuccess')
  @@ -339,9 +341,11 @@ exports.flash = (image, drives) => {
  * imageWriter.cancel()
  */
  exports.cancel = () => {
  + const drives = selectionState.getSelectedDevices()
  analytics.logEvent('Cancel', {
  image: selectionState.getImagePath(),
  - drives: selectionState.getSelectedDevices(),
  + drives,
  + driveCount: drives.length,
  uuid: flashState.getFlashUuid(),
  unmountOnSuccess: settings.get('unmountOnSuccess'),
  validateWriteOnSuccess: settings.get('validateWriteOnSuccess')
  