cros: Don't attempt to focus OOBE dialog if it is not showing

This prevents an invalid request while in the lock screen, since the OOBE
dialog does not exist.

Bug: 905752
Change-Id: Ie1f820877ea659c9cbfa1e260c2e6a49776e46c9
Reviewed-on: https://chromium-review.googlesource.com/c/1338111Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608903}

ash/shelf/login_shelf_view.cc

@@ -393,8 +393,12 @@ void LoginShelfView::AboutToRequestFocusFromTabTraversal(bool reverse) {
     // Focus should leave the system tray.
     Shell::Get()->system_tray_notifier()->NotifyFocusOut(reverse);
 
-    // If OOBE dialog is showing, it will take focus.
-    Shell::Get()->login_screen_controller()->FocusOobeDialog();
+    // If the dialog is hidden, let views handle the focus automatically.
+    // Otherwise, forward a focus request to the OOBE dialog.
+    if (dialog_state_ != mojom::OobeDialogState::HIDDEN &&
+        dialog_state_ != mojom::OobeDialogState::NONE) {
+      Shell::Get()->login_screen_controller()->FocusOobeDialog();
+    }
   } else {
     // Focus goes to status area.
     Shelf::ForWindow(GetWidget()->GetNativeWindow())