Use ScopedTaskEnvironment instead of MessageLoopForUI in ui/aura/test/.

ui/aura/test/aura_test_helper.cc

 // Copyright (c) 2012 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 "ui/aura/test/aura_test_helper.h"
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "ui/aura/client/default_capture_client.h"
 #include "ui/aura/client/focus_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/input_state_lookup.h"
 #include "ui/aura/mus/capture_synchronizer.h"
 #include "ui/aura/mus/focus_synchronizer.h"
 #include "ui/aura/mus/window_port_mus.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/test/env_test_helper.h"
@@ skipping 21 matching lines @@
 #endif
 
 namespace aura {
 namespace test {
 namespace {
 
 AuraTestHelper* g_instance = nullptr;
 
 }  // namespace
 
-AuraTestHelper::AuraTestHelper(base::MessageLoopForUI* message_loop)
+AuraTestHelper::AuraTestHelper()
     : setup_called_(false), teardown_called_(false) {
-  DCHECK(message_loop);
   // Disable animations during tests.
   zero_duration_mode_.reset(new ui::ScopedAnimationDurationScaleMode(
       ui::ScopedAnimationDurationScaleMode::ZERO_DURATION));
   ui::test::EnableTestConfigForPlatformWindows();
   InitializeAuraEventGeneratorDelegate();
 }
 
 AuraTestHelper::~AuraTestHelper() {
   CHECK(setup_called_)
       << "AuraTestHelper::SetUp() never called.";
@@ skipping 138 matching lines @@
   window_tree_client_setup_ = base::MakeUnique<TestWindowTreeClientSetup>();
   window_tree_client_setup_->InitForWindowManager(window_tree_delegate_,
                                                   window_manager_delegate_);
   window_tree_client_ = window_tree_client_setup_->window_tree_client();
   window_tree_client_->capture_synchronizer()->AttachToCaptureClient(
       capture_client_.get());
 }
 
 }  // namespace test
 }  // namespace aura