Factor draw functionality out of DefaultPlatformDisplay into FrameGenerator.

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 "base/memory/ptr_util.h"
 #include "cc/output/copy_output_request.h"
 #include "services/shell/public/interfaces/connector.mojom.h"
 #include "services/ui/surfaces/surfaces_state.h"
 #include "services/ui/ws/display_binding.h"
 #include "services/ui/ws/display_manager.h"
+#include "services/ui/ws/platform_display_init_params.h"
 #include "services/ui/ws/server_window_surface_manager_test_api.h"
 #include "services/ui/ws/window_manager_access_policy.h"
 #include "services/ui/ws/window_manager_window_tree_factory.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace ui {
 namespace ws {
 namespace test {
 namespace {
 
@@ skipping 464 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