mash: Relay some Chrome aura window properties to Ash.

ui/views/mus/mus_client.h

Index: ui/views/mus/mus_client.h
diff --git a/ui/views/mus/mus_client.h b/ui/views/mus/mus_client.h
index 72792a72c520077a42ff6d760307bdc04bb16de2..62e0a30be142112862b5ab6e6d4f5cedcc45089f 100644
--- a/ui/views/mus/mus_client.h
+++ b/ui/views/mus/mus_client.h
@@ -58,8 +58,7 @@ class MusClientTestApi;
 
 // MusClient establishes a connection to mus and sets up necessary state so that
 // aura and views target mus. This class is useful for typical clients, not the
-// WindowManager. Most clients don't create this directly, rather use
-// AuraInit.
+// WindowManager. Most clients don't create this directly, rather use AuraInit.
 class VIEWS_MUS_EXPORT MusClient
     : public aura::WindowTreeClientDelegate,
       public ScreenMusDelegate,
@@ -104,6 +103,9 @@ class VIEWS_MUS_EXPORT MusClient
   void AddObserver(MusClientObserver* observer);
   void RemoveObserver(MusClientObserver* observer);
 
+  // Called when a client window property changes; notifies observers.
+  void OnWindowPropertyChanged(aura::Window* window, const void* key);
+
  private:
   friend class AuraInit;
   friend class test::MusClientTestApi;