WIP: Propagate SurfaceID up window tree hierarchy

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 42807955e82786a5f8674f19d483439130bd9d34..25c7cdfd2508cf6dc86a9261699ac22d9a87eedc 100644
--- a/services/ui/ws/display.cc
+++ b/services/ui/ws/display.cc
@@ -285,6 +285,13 @@ void Display::CreateWindowManagerDisplayRootFromFactory(
       std::move(display_root_ptr));
 }
 
+ServerWindow* Display::GetActiveRootWindow() {
+  WindowManagerDisplayRoot* display_root = GetActiveWindowManagerDisplayRoot();
+  if (display_root)
+    return display_root->root();
+  return nullptr;
+}
+
 ServerWindow* Display::GetRootWindow() {
   return root_.get();
 }