aura-mus: Implement Deactivate().

ui/views/widget/desktop_aura/desktop_native_widget_aura.cc

Index: ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
diff --git a/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc b/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
index 21aca730c6e063afb1c2c657c70693f65a63c906..f442ef1c3cc4400cfc8a4426e465a23510825580 100644
--- a/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
+++ b/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
@@ -1104,6 +1104,10 @@ void DesktopNativeWidgetAura::OnWindowActivated(
     // Pass in false so that ClearNativeFocus() isn't invoked.
     GetWidget()->GetFocusManager()->StoreFocusedView(false);
   }
+
+  // Give the native widget a chance to handle any specific changes it needs.
+  desktop_window_tree_host_->OnNativeWidgetActivationChanged(
+      content_window_ == gained_active);
 }
 
 ////////////////////////////////////////////////////////////////////////////////