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

ui/aura/test/aura_test_helper.h

 // 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.
 
 #ifndef UI_AURA_TEST_AURA_TEST_HELPER_H_
 #define UI_AURA_TEST_AURA_TEST_HELPER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_tree_host.h"
 
-namespace base {
-class MessageLoopForUI;
-}
-
 namespace ui {
 class ContextFactory;
 class ScopedAnimationDurationScaleMode;
 }
 
 namespace wm {
 class WMState;
 }
 
 namespace aura {
@@ skipping 12 matching lines @@
 class FocusClient;
 }
 namespace test {
 class TestWindowParentingClient;
 
 // A helper class owned by tests that does common initialization required for
 // Aura use. This class creates a root window with clients and other objects
 // that are necessary to run test on Aura.
 class AuraTestHelper {
  public:
-  explicit AuraTestHelper(base::MessageLoopForUI* message_loop);
+  AuraTestHelper();
   ~AuraTestHelper();
 
   // Returns the current AuraTestHelper, or nullptr if it's not alive.
   static AuraTestHelper* GetInstance();
 
   // Makes aura target mus with a mock WindowTree (TestWindowTree). Must be
   // called before SetUp().
   void EnableMusWithTestWindowTree(
       WindowTreeClientDelegate* window_tree_delegate,
       WindowManagerDelegate* window_manager_delegate);
@@ skipping 65 matching lines @@
 
   WindowTreeClient* window_tree_client_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(AuraTestHelper);
 };
 
 }  // namespace test
 }  // namespace aura
 
 #endif  // UI_AURA_TEST_AURA_TEST_HELPER_H_