mash: wires up shadows for mash

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 4a7616abc7bfe70c5bf218eba6c718084b3fe491..c8633b68fad2697338441c0464de0808585d5a71 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host.h
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host.h
@@ -167,6 +167,9 @@ class VIEWS_EXPORT DesktopWindowTreeHost {
   // used, a return value of false indicates the DesktopWindowTreeHost manages
   // cursors itself.
   virtual bool ShouldUseDesktopNativeCursorManager() const = 0;
+
+  // Returns whether a VisibilityController should be created.
+  virtual bool ShouldCreateVisibilityController() const = 0;
 };
 
 }  // namespace views