Use ScopedTaskEnvironment instead of MessageLoopForUI in ui tests.

ui/message_center/cocoa/popup_collection_unittest.mm

 // Copyright (c) 2013 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.
 
 #import "ui/message_center/cocoa/popup_collection.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/mac/scoped_nsobject.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/scoped_task_environment.h"
 #import "ui/gfx/test/ui_cocoa_test_helper.h"
 #import "ui/message_center/cocoa/notification_controller.h"
 #import "ui/message_center/cocoa/popup_controller.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_style.h"
 #include "ui/message_center/notification.h"
 
 using base::ASCIIToUTF16;
 
 namespace message_center {
 
 class PopupCollectionTest : public ui::CocoaTest {
  public:
-  PopupCollectionTest() {
+  PopupCollectionTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI) {
     message_center::MessageCenter::Initialize();
     center_ = message_center::MessageCenter::Get();
     collection_.reset(
         [[MCPopupCollection alloc] initWithMessageCenter:center_]);
     [collection_ setAnimationDuration:0.001];
     [collection_ setAnimationEndedCallback:^{
         if (nested_run_loop_.get())
           nested_run_loop_->Quit();
     }];
   }
@@ skipping 49 matching lines @@
   }
 
   void WaitForAnimationEnded() {
     if (![collection_ isAnimating])
       return;
     nested_run_loop_.reset(new base::RunLoop());
     nested_run_loop_->Run();
     nested_run_loop_.reset();
   }
 
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::unique_ptr<base::RunLoop> nested_run_loop_;
   message_center::MessageCenter* center_;
   base::scoped_nsobject<MCPopupCollection> collection_;
 };
 
 TEST_F(PopupCollectionTest, AddThreeCloseOne) {
   EXPECT_EQ(0u, [[collection_ popups] count]);
   AddThreeNotifications();
   EXPECT_EQ(3u, [[collection_ popups] count]);
 
@@ skipping 228 matching lines @@
       ASCIIToUTF16("New message."), gfx::Image(), base::string16(), GURL(),
       DummyNotifierId(), message_center::RichNotificationData(), NULL));
   center_->UpdateNotification("1", std::move(notification));
 
   // Release the popup collection before the animation ends. No crash should
   // be expected.
   collection_.reset();
 }
 
 }  // namespace message_center