Merge pull request #12619 from electron/add-before-update-event

add new event to auto-updater

atom/browser/api/atom_api_auto_updater.cc

@@ -104,6 +104,8 @@ void AutoUpdater::SetFeedURL(mate::Arguments* args) {
 }
 
 void AutoUpdater::QuitAndInstall() {
+  Emit("before-quit-for-update");
+
   // If we don't have any window then quitAndInstall immediately.
   if (WindowList::IsEmpty()) {
     auto_updater::AutoUpdater::QuitAndInstall();