Fix GPU service and display initialization race.

services/ui/ws/test_utils.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "services/ui/ws/test_utils.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "cc/output/copy_output_request.h"
@@ skipping 399 matching lines @@
     AddDisplay();
 }
 
 Display* TestWindowServerDelegate::AddDisplay() {
   // Display manages its own lifetime.
   Display* display = new Display(window_server_, PlatformDisplayInitParams());
   display->Init(nullptr);
   return display;
 }
 
+void TestWindowServerDelegate::StartDisplayInit() {}
+
 void TestWindowServerDelegate::OnNoMoreDisplays() {
   got_on_no_more_displays_ = true;
 }
 
 std::unique_ptr<WindowTreeBinding>
 TestWindowServerDelegate::CreateWindowTreeBinding(
     BindingType type,
     ws::WindowServer* window_server,
     ws::WindowTree* tree,
     mojom::WindowTreeRequest* tree_request,
@@ skipping 146 matching lines @@
     return nullptr;
   if (!tree->AddWindow(parent_client_id, client_window_id))
     return nullptr;
   *client_id = client_window_id;
   return tree->GetWindowByClientId(client_window_id);
 }
 
 }  // namespace test
 }  // namespace ws
 }  // namespace ui