cros: Don't request menu items twice.

During long press, we request menu options twice. Avoid making this
expensive call twice.

Before, we returned early on the callback. Keep that incase race
conditions, but also return early before the request if a menu already
exists.

Bug: 907556
Change-Id: Ie7798e25faea5128651f4a06415d978a5a6cbe35
Reviewed-on: https://chromium-review.googlesource.com/c/1347090Reviewed-by: Weidong Guo <weidongg@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610113}

ash/app_list/views/app_list_item_view.cc

@@ -494,6 +494,8 @@ void AppListItemView::OnContextMenuModelReceived(
 void AppListItemView::ShowContextMenuForView(views::View* source,
                                              const gfx::Point& point,
                                              ui::MenuSourceType source_type) {
+  if (context_menu_ && context_menu_->IsShowingMenu())
+    return;
   // Prevent multiple requests for context menus before the current request
   // completes. If a second request is sent before the first one can respond,
   // the Chrome side delegate will become unresponsive