mash: Preliminary support for widget hit test masks

components/mus/ws/window_tree.h

Index: components/mus/ws/window_tree.h
diff --git a/components/mus/ws/window_tree.h b/components/mus/ws/window_tree.h
index 143fa940cb673e3e8085e3509f71c1a6b8f0e22d..bd6016361340a6e13228a3cf4783d60def09715c 100644
--- a/components/mus/ws/window_tree.h
+++ b/components/mus/ws/window_tree.h
@@ -381,6 +381,7 @@ class WindowTree : public mojom::WindowTree,
       Id transport_window_id,
       mojo::InsetsPtr insets,
       mojo::Array<mojo::RectPtr> transport_additional_client_areas) override;
+  void SetHitTestMask(Id transport_window_id, mojo::RectPtr mask) override;
   void GetWindowManagerClient(
       mojo::AssociatedInterfaceRequest<mojom::WindowManagerClient> internal)
       override;