mash: Preliminary support for widget hit test masks

components/mus/public/cpp/lib/window.cc

Index: components/mus/public/cpp/lib/window.cc
diff --git a/components/mus/public/cpp/lib/window.cc b/components/mus/public/cpp/lib/window.cc
index c5a3c310253f2b1e06adea6816d04450505a7cde..7802e6837a6fa580ed60e31d80bc22c9c54aab68 100644
--- a/components/mus/public/cpp/lib/window.cc
+++ b/components/mus/public/cpp/lib/window.cc
@@ -217,6 +217,15 @@ void Window::SetClientArea(
   LocalSetClientArea(client_area, additional_client_areas);
 }
 
+void Window::SetHitTestMask(const gfx::Rect& mask) {
+  if (!OwnsWindowOrIsRoot(this))
+    return;
+
+  if (connection_)
+    tree_client()->SetHitTestMask(server_id_, mask);
+  hit_test_mask_ = mask;
+}
+
 void Window::SetVisible(bool value) {
   if (visible_ == value)
     return;