mash: Convert OnWindowInputEventAck to use an enum for handled status

ui/views/mus/platform_window_mus.h

Index: ui/views/mus/platform_window_mus.h
diff --git a/ui/views/mus/platform_window_mus.h b/ui/views/mus/platform_window_mus.h
index 7e9caa0961ba675d4e4fac68c1aca0e6627fb862..9364239879998bc6493194450c2b303e73a33d68 100644
--- a/ui/views/mus/platform_window_mus.h
+++ b/ui/views/mus/platform_window_mus.h
@@ -86,7 +86,8 @@ class VIEWS_MUS_EXPORT PlatformWindowMus
   void OnWindowInputEvent(
       mus::Window* view,
       const ui::Event& event,
-      std::unique_ptr<base::Callback<void(bool)>>* ack_callback) override;
+      std::unique_ptr<base::Callback<void(mus::mojom::EventResult)>>*
+          ack_callback) override;
 
   ui::PlatformWindowDelegate* delegate_;
   mus::Window* mus_window_;