mus: Changes SetDisplayRoot() to create actual display

services/ui/ws/display_manager.cc

Index: services/ui/ws/display_manager.cc
diff --git a/services/ui/ws/display_manager.cc b/services/ui/ws/display_manager.cc
index 2bde1589308aa5deba4d51f0c43b8ea364ac6947..286993ece49f719e85e779983db9d3e10b488f2e 100644
--- a/services/ui/ws/display_manager.cc
+++ b/services/ui/ws/display_manager.cc
@@ -77,6 +77,12 @@ void DisplayManager::AddDisplay(Display* display) {
   pending_displays_.insert(display);
 }
 
+void DisplayManager::AddDisplayForWindowManager(
+    const display::Display& display,
+    const display::ViewportMetrics& metrics) {
+  OnDisplayAdded(display, metrics);
+}
+
 void DisplayManager::DestroyDisplay(Display* display) {
   if (pending_displays_.count(display)) {
     pending_displays_.erase(display);