mash: Preliminary support for widget hit test masks

components/mus/public/cpp/lib/window_tree_client_impl.h

Index: components/mus/public/cpp/lib/window_tree_client_impl.h
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.h b/components/mus/public/cpp/lib/window_tree_client_impl.h
index aef326f7cc320d143bfa1368f37c5eb1f81415f7..9736b642f7b33cf40f2834e2a48a547c5ebb5abd 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.h
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.h
@@ -87,6 +87,7 @@ class WindowTreeClientImpl : public WindowTreeConnection,
   void SetClientArea(Id window_id,
                      const gfx::Insets& client_area,
                      const std::vector<gfx::Rect>& additional_client_areas);
+  void SetHitTestMask(Id window_id, const gfx::Rect& mask);
   void SetFocus(Window* window);
   void SetCanFocus(Id window_id, bool can_focus);
   void SetPredefinedCursor(Id window_id, mus::mojom::Cursor cursor_id);