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

services/ui/ws/display.cc

Index: services/ui/ws/display.cc
diff --git a/services/ui/ws/display.cc b/services/ui/ws/display.cc
index 6314eb33cc1079fcc9b016fe8b39ece56a226428..8a9cf9838f4a616d5e3400a7576cbfe5445d7bda 100644
--- a/services/ui/ws/display.cc
+++ b/services/ui/ws/display.cc
@@ -271,6 +271,13 @@ ServerWindow* Display::GetRootWindow() {
   return root_.get();
 }
 
+ServerWindow* Display::GetActiveRootWindow() {
+  WindowManagerDisplayRoot* display_root = GetActiveWindowManagerDisplayRoot();
+  if (display_root)
+    return display_root->root();
+  return nullptr;
+}
+
 void Display::OnAcceleratedWidgetAvailable() {
   display_manager()->OnDisplayAcceleratedWidgetAvailable(this);
   InitWindowManagerDisplayRoots();