Enables passing initial properties to top level window creation

ui/aura/mus/window_port_mus.h

Index: ui/aura/mus/window_port_mus.h
diff --git a/ui/aura/mus/window_port_mus.h b/ui/aura/mus/window_port_mus.h
index 7adcdedee8fd9b6f3cc01d0d9abaae9efb231f06..a4bbd525b4f20b51a312f5608e7de36565c0f725 100644
--- a/ui/aura/mus/window_port_mus.h
+++ b/ui/aura/mus/window_port_mus.h
@@ -30,6 +30,7 @@ class Window;
 class WindowPortMusTestApi;
 class WindowTreeClient;
 class WindowTreeClientPrivate;
+class WindowTreeHostMus;
 
 // WindowPortMus is a WindowPort that forwards calls to WindowTreeClient
 // so that changes are propagated to the server. All changes from
@@ -71,6 +72,7 @@ class AURA_EXPORT WindowPortMus : public WindowPort, public WindowMus {
   friend class WindowPortMusTestApi;
   friend class WindowTreeClient;
   friend class WindowTreeClientPrivate;
+  friend class WindowTreeHostMus;
 
   using ServerChangeIdType = uint8_t;