mus: Make sure window parenting happens in the window server.

services/ui/ws/window_server.cc

Index: services/ui/ws/window_server.cc
diff --git a/services/ui/ws/window_server.cc b/services/ui/ws/window_server.cc
index 651eb157e9b46ff77ddaf87b626ae6e22db48aba..7e8d355eb252189a7b3b01dedc4b10f99911a1bf 100644
--- a/services/ui/ws/window_server.cc
+++ b/services/ui/ws/window_server.cc
@@ -509,6 +509,13 @@ WindowTree* WindowServer::GetCurrentDragLoopInitiator() {
 void WindowServer::OnDisplayReady(Display* display, bool is_first) {
   if (is_first)
     delegate_->OnFirstDisplayReady();
+  gpu_host_->OnAcceleratedWidgetAvailable(
+      display->platform_display()->GetAcceleratedWidget());
+}
+
+void WindowServer::OnDisplayDestroyed(Display* display) {
+  gpu_host_->OnAcceleratedWidgetDestroyed(
+      display->platform_display()->GetAcceleratedWidget());
 }
 
 void WindowServer::OnNoMoreDisplays() {