aura-mus: Implement Deactivate().

ui/views/widget/desktop_aura/desktop_window_tree_host.h

Index: ui/views/widget/desktop_aura/desktop_window_tree_host.h
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host.h b/ui/views/widget/desktop_aura/desktop_window_tree_host.h
index cdf5be905ff7d27a04fea5af3bf344b3f6db7ed6..4a7616abc7bfe70c5bf218eba6c718084b3fe491 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host.h
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host.h
@@ -57,6 +57,9 @@ class VIEWS_EXPORT DesktopWindowTreeHost {
   // Called from DesktopNativeWidgetAura::OnWidgetInitDone().
   virtual void OnWidgetInitDone() = 0;
 
+  // Called from DesktopNativeWidgetAura::OnWindowActivated().
+  virtual void OnNativeWidgetActivationChanged(bool active) = 0;
+
   // Creates and returns the Tooltip implementation to use. Return value is
   // owned by DesktopNativeWidgetAura and lives as long as
   // DesktopWindowTreeHost.