Demonstrate external-window-mode in mus-demo

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 f4d960a65c3c858f7f588d525afbef07bb726961..f034ff54d8246acaa3a38f4ff51b536b809997b3 100644
--- a/services/ui/ws/window_server.cc
+++ b/services/ui/ws/window_server.cc
@@ -760,7 +760,14 @@ void WindowServer::OnGpuServiceInitialized() {
       display_compositor_client_binding_.CreateInterfacePtrAndBind());
   // TODO(kylechar): When gpu channel is removed, this can instead happen
   // earlier, after GpuServiceProxy::OnInitialized().
-  delegate_->StartDisplayInit();
+  bool window_manager_connected = false;
+  for (auto* factory : window_manager_window_tree_factory_set_.GetFactories()) {
+    if (factory->window_tree()) {
+      window_manager_connected = true;
+      break;
+    }
+  }
+  delegate_->StartDisplayInit(window_manager_connected);
 }
 
 void WindowServer::OnSurfaceCreated(const cc::SurfaceId& surface_id,