LoginUserMenuView: Fix focus for remove user button

Tab keystroke from user options menu on a lock screen should move focus
to the next available user pod or "Shut down" button, if there is no
more user pods in a row. Also focus should stay in a dropdown menu, if
keys other than Tab or Escape are pressed.

Previously any keystroke from the “Remove account” button inside the
dropdown menu has always moved focus to the “Shut down” button.

Bug: 1107667
Change-Id: I8b0579e477b9f055ead9cd13e06a88982ab31db1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2418572Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Danila Kuzmin <dkuzmin@google.com>
Cr-Commit-Position: refs/heads/master@{#810161}

ash/login/ui/login_user_menu_view.cc

@@ -63,16 +63,16 @@ class RemoveUserButton : public SystemLabelButton {
       return;
     }
 
-    if (event->key_code() != ui::VKEY_RETURN) {
-      // The remove-user button should handle bubble dismissal and stop
-      // propagation, otherwise the event will propagate to the bubble widget,
-      // which will close itself and invalidate the bubble pointer in
-      // LoginUserMenuView.
-      event->StopPropagation();
+    if (event->key_code() == ui::VKEY_ESCAPE ||
+        event->key_code() == ui::VKEY_TAB) {
       bubble_->Hide();
-    } else {
-      views::Button::OnKeyEvent(event);
+      // We explicitly move focus back to the dropdown button so the Tab
+      // traversal works correctly.
+      bubble_->GetBubbleOpener()->RequestFocus();
     }
+
+    if (event->key_code() == ui::VKEY_RETURN)
+      views::Button::OnKeyEvent(event);
   }
 
   LoginUserMenuView* bubble_;