oobe: Fix focus traversal for screens with invisible status area

Sometimes there is no status area shown on the screen and we need to
check it during tab traversal.

Bug: 1008817
Change-Id: If6099f8c020818de62a3bc2bccbe07f077817d52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551120Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Danila Kuzmin <dkuzmin@google.com>
Cr-Commit-Position: refs/heads/master@{#830962}

ash/login/login_screen_controller.cc

@@ -289,16 +289,22 @@ void LoginScreenController::FocusLoginShelf(bool reverse) {
   Shelf* shelf = Shelf::ForWindow(Shell::Get()->GetPrimaryRootWindow());
   // Tell the focus direction to the status area or the shelf so they can focus
   // the correct child view.
-  if (reverse || !shelf->shelf_widget()->login_shelf_view()->IsFocusable()) {
-    if (!Shell::GetPrimaryRootWindowController()->IsSystemTrayVisible())
-      return;
+  if (Shell::GetPrimaryRootWindowController()->IsSystemTrayVisible() &&
+      (reverse || !shelf->shelf_widget()->login_shelf_view()->IsFocusable())) {
+    // Focus goes to system tray (status area) if one of the following is true:
+    //  - system tray is visible and tab is in reverse order;
+    //  - system tray is visible and there is no visible shelf buttons before.
     shelf->GetStatusAreaWidget()
         ->status_area_widget_delegate()
         ->set_default_last_focusable_child(reverse);
     Shell::Get()->focus_cycler()->FocusWidget(shelf->GetStatusAreaWidget());
-  } else {
+  } else if (shelf->shelf_widget()->login_shelf_view()->IsFocusable()) {
+    // Otherwise focus goes to shelf buttons when there is any.
     shelf->shelf_widget()->set_default_last_focusable_child(reverse);
     Shell::Get()->focus_cycler()->FocusWidget(shelf->shelf_widget());
+  } else {
+    // No elements to focus on the shelf.
+    NOTREACHED();
   }
 }
 

ash/shelf/login_shelf_view.cc

@@ -579,12 +579,16 @@ void LoginShelfView::AboutToRequestFocusFromTabTraversal(bool reverse) {
     // Focus should leave the system tray.
     Shell::Get()->system_tray_notifier()->NotifyFocusOut(reverse);
   } else {
-    // Focus goes to status area.
     StatusAreaWidget* status_area_widget =
         Shelf::ForWindow(GetWidget()->GetNativeWindow())->GetStatusAreaWidget();
-    status_area_widget->status_area_widget_delegate()
-        ->set_default_last_focusable_child(reverse);
-    Shell::Get()->focus_cycler()->FocusWidget(status_area_widget);
+    // Focus goes to status area if it is visible.
+    if (status_area_widget->IsVisible()) {
+      status_area_widget->status_area_widget_delegate()
+          ->set_default_last_focusable_child(reverse);
+      Shell::Get()->focus_cycler()->FocusWidget(status_area_widget);
+    } else {
+      Shell::Get()->system_tray_notifier()->NotifyFocusOut(reverse);
+    }
   }
 }