Ash Tray: Fix quick settings not closing after clicking on a notification.

This is a reland of the original fix (see bug), which was reverted due to
regressions.

This updated version fixes an edge case, which caused a crash when dismissing
the message center via accelerator in certian circumstances.

BUG=1024100

Change-Id: I525186a7075732946403ebffa5def4631bcde658
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2013525Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Commit-Queue: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733852}

ash/system/unified/unified_system_tray_bubble.cc

@@ -319,19 +319,21 @@ void UnifiedSystemTrayBubble::OnWindowActivated(ActivationReason reason,
     return;
   }
 
-  // Don't close the bubble if the message center is gaining or losing
-  // activation.
+  // Don't close the bubble if the message center is gaining 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))) {
+        views::Widget::GetWidgetForNativeView(gained_active)) {
       return;
     }
+
+    // If the message center is not visible, ignore activation changes.
+    // Otherwise, this may cause a crash when closing the dialog via
+    // accelerator. See crbug.com/1041174.
+    if (!message_center_widget->IsVisible())
+      return;
   }
 
   tray_->CloseBubble();