Reland of "Mustash: Ensure surfaces submitted to Mus by WM and embedders contain Surfaces with embe…

services/ui/ws/platform_display_default.cc

Index: services/ui/ws/platform_display_default.cc
diff --git a/services/ui/ws/platform_display_default.cc b/services/ui/ws/platform_display_default.cc
index 6a3a6e9dc9fb2d7e4cf40f969ea54d24801fecbe..e69588ed97f1f3404e5fa78fa4f528f2e839c861 100644
--- a/services/ui/ws/platform_display_default.cc
+++ b/services/ui/ws/platform_display_default.cc
@@ -248,6 +248,10 @@ void PlatformDisplayDefault::OnAcceleratedWidgetDestroyed() {
 
 void PlatformDisplayDefault::OnActivationChanged(bool active) {}
 
+ServerWindow* PlatformDisplayDefault::GetActiveRootWindow() {
+  return delegate_->GetActiveRootWindow();
+}
+
 bool PlatformDisplayDefault::IsInHighContrastMode() {
   return delegate_ ? delegate_->IsInHighContrastMode() : false;
 }