Fix GPU service and display initialization race.

services/ui/ws/window_server_delegate.h

Index: services/ui/ws/window_server_delegate.h
diff --git a/services/ui/ws/window_server_delegate.h b/services/ui/ws/window_server_delegate.h
index 50ae3aae3614683f4034d03a117e954e13de60af..802dbd77dd69f44d42898cac949265ab622c6fda 100644
--- a/services/ui/ws/window_server_delegate.h
+++ b/services/ui/ws/window_server_delegate.h
@@ -36,6 +36,9 @@ class WindowServerDelegate {
     WINDOW_MANAGER,
   };
 
+  // WindowServer signal that display initialization can start.
+  virtual void StartDisplayInit() = 0;
+
   // Called once when the AcceleratedWidget of a Display is available.
   virtual void OnFirstDisplayReady();