Fixes bug where NonClientFrameController wasn't registered correctly

ash/mus/non_client_frame_controller.cc

Index: ash/mus/non_client_frame_controller.cc
diff --git a/ash/mus/non_client_frame_controller.cc b/ash/mus/non_client_frame_controller.cc
index 58cdbf84ec832a8297e24adeaabc810a233da2a1..784bd44190c46f2660f413f5f00139240d3d47d4 100644
--- a/ash/mus/non_client_frame_controller.cc
+++ b/ash/mus/non_client_frame_controller.cc
@@ -308,6 +308,7 @@ NonClientFrameController::NonClientFrameController(
       widget_, window_manager_client_, ShouldRemoveStandardFrame(*properties),
       ShouldEnableImmersive(*properties));
   window_ = native_widget->GetNativeView();
+  window_->SetProperty(kNonClientFrameControllerKey, this);
   window_->SetProperty(kWidgetCreationTypeKey, WidgetCreationType::FOR_CLIENT);
   window_->AddObserver(this);
   params.native_widget = native_widget;