Use ScopedTaskEnvironment instead of MessageLoopForUI in ui tests.

ui/aura/mus/os_exchange_data_provider_mus_unittest.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 "ui/aura/mus/os_exchange_data_provider_mus.h"
 
 #include <memory>
 
 #include "base/files/file_util.h"
 #include "base/memory/ptr_util.h"
-#include "base/message_loop/message_loop.h"
 #include "base/pickle.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/scoped_task_environment.h"
 #include "build/build_config.h"
 #include "net/base/filename_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 #include "ui/base/dragdrop/os_exchange_data.h"
 #include "ui/base/dragdrop/os_exchange_data_provider_factory.h"
 #include "ui/events/platform/platform_event_source.h"
 #include "url/gurl.h"
 
 using ui::Clipboard;
 using ui::OSExchangeData;
 
 namespace aura {
 
 // This file is a copy/paste of the unit tests in os_exchange_data_unittest.cc,
 // with additional SetUp() to force the mus override. I thought about changeing
 // the OSExchangeData test suite to a parameterized test suite, but I've
 // previously had problems with that feature of gtest.
 
 class OSExchangeDataProviderMusTest
     : public PlatformTest,
       public ui::OSExchangeDataProviderFactory::Factory {
  public:
-  OSExchangeDataProviderMusTest() {}
+  OSExchangeDataProviderMusTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI) {}
 
   // Overridden from PlatformTest:
   void SetUp() override {
     PlatformTest::SetUp();
     old_factory_ = ui::OSExchangeDataProviderFactory::TakeFactory();
     ui::OSExchangeDataProviderFactory::SetFactory(this);
   }
 
   void TearDown() override {
     ui::OSExchangeDataProviderFactory::TakeFactory();
     ui::OSExchangeDataProviderFactory::SetFactory(old_factory_);
     PlatformTest::TearDown();
   }
 
   // Overridden from ui::OSExchangeDataProviderFactory::Factory:
   std::unique_ptr<OSExchangeData::Provider> BuildProvider() override {
     return base::MakeUnique<OSExchangeDataProviderMus>();
   }
 
  private:
   ui::OSExchangeDataProviderFactory::Factory* old_factory_ = nullptr;
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 TEST_F(OSExchangeDataProviderMusTest, StringDataGetAndSet) {
   OSExchangeData data;
   base::string16 input = base::ASCIIToUTF16("I can has cheezburger?");
   EXPECT_FALSE(data.HasString());
   data.SetString(input);
   EXPECT_TRUE(data.HasString());
 
   OSExchangeData data2(
@@ skipping 133 matching lines @@
   data.SetHtml(html, url);
 
   OSExchangeData copy(
       std::unique_ptr<OSExchangeData::Provider>(data.provider().Clone()));
   base::string16 read_html;
   EXPECT_TRUE(copy.GetHtml(&read_html, &url));
   EXPECT_EQ(html, read_html);
 }
 
 }  // namespace aura