Use ScopedTaskEnvironment instead of MessageLoopForUI in ui tests.

ui/base/dragdrop/os_exchange_data_unittest.cc

 // Copyright 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.
 
 #include <memory>
 
 #include "base/files/file_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/events/platform/platform_event_source.h"
 #include "url/gurl.h"
 
 namespace ui {
 
 class OSExchangeDataTest : public PlatformTest {
  public:
   OSExchangeDataTest()
-      : event_source_(ui::PlatformEventSource::CreateDefault()) {}
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI),
+        event_source_(ui::PlatformEventSource::CreateDefault()) {}
 
  private:
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::unique_ptr<PlatformEventSource> event_source_;
 };
 
 TEST_F(OSExchangeDataTest, StringDataGetAndSet) {
   OSExchangeData data;
   base::string16 input = base::ASCIIToUTF16("I can has cheezburger?");
   EXPECT_FALSE(data.HasString());
   data.SetString(input);
   EXPECT_TRUE(data.HasString());
 
@@ skipping 136 matching lines @@
 
   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);
 }
 #endif
 
 }  // namespace ui