Fix message center crash

Modify check for message center gaining activation to not
dereference the message center widget. There's a crash
caused by focus switching between the message center
and quick setting bubbles before the message center bubble's
constructor has exited.

Change-Id: Ia15acb47dc3806466a2f40a73e843333655e7953
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1860692
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Reviewed-by: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705749}

ash/system/unified/unified_system_tray_bubble.cc

@@ -299,15 +299,9 @@ void UnifiedSystemTrayBubble::OnWindowActivated(ActivationReason reason,
 
   // Don't close the bubble if the message center is gaining or losing
   // activation.
-  if (features::IsUnifiedMessageCenterRefactorEnabled() &&
-      tray_->IsMessageCenterBubbleShown()) {
-    views::Widget* message_center_widget =
-        tray_->message_center_bubble()->GetBubbleWidget();
-    if (message_center_widget ==
-            views::Widget::GetWidgetForNativeView(gained_active) ||
-        (lost_active &&
-         message_center_widget ==
-             views::Widget::GetWidgetForNativeView(lost_active))) {
+  if (features::IsUnifiedMessageCenterRefactorEnabled()) {
+    if (GetContainerForWindow(gained_active) ==
+        GetContainerForWindow(lost_active)) {
       return;
     }
   }