mus: Client-side implementation of modal windows

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

Index: components/mus/public/cpp/lib/window_tree_client_impl.cc
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.cc b/components/mus/public/cpp/lib/window_tree_client_impl.cc
index cdcd7b613a8670b7c973c2d8ac8c887086c01b92..47ea48ee4cc87d9d8fb68a1fa5b16597c3efd238 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.cc
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.cc
@@ -217,6 +217,13 @@ void WindowTreeClientImpl::RemoveTransientWindowFromParent(Window* window) {
   tree_->RemoveTransientWindowFromParent(change_id, window->id());
 }
 
+void WindowTreeClientImpl::SetModal(Window* window) {
+  DCHECK(tree_);
+  const uint32_t change_id = ScheduleInFlightChange(
+      make_scoped_ptr(new CrashInFlightChange(window, ChangeType::SET_MODAL)));
+  tree_->SetModal(change_id, window->id());
+}
+
 void WindowTreeClientImpl::Reorder(Window* window,
                                    Id relative_window_id,
                                    mojom::OrderDirection direction) {