Use ScopedTaskEnvironment instead of MessageLoopForUI in components tests.

components/arc/arc_session_runner_unittest.cc

 // Copyright 2015 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 <utility>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback_helpers.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
+#include "base/test/scoped_task_environment.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "components/arc/arc_session_runner.h"
 #include "components/arc/test/fake_arc_session.h"
 #include "mojo/public/cpp/system/message_pipe.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace arc {
 
 namespace {
 
 class DoNothingObserver : public ArcSessionRunner::Observer {
  public:
   void OnSessionStopped(ArcStopReason reason, bool restarting) override {
     // Do nothing.
   }
 };
 
 }  // namespace
 
 class ArcSessionRunnerTest : public testing::Test,
                              public ArcSessionRunner::Observer {
  public:
-  ArcSessionRunnerTest() = default;
+  ArcSessionRunnerTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI) {}
 
   void SetUp() override {
     chromeos::DBusThreadManager::Initialize();
 
     stop_reason_ = ArcStopReason::SHUTDOWN;
     restarting_ = false;
 
     // We inject FakeArcSession here so we do not need task_runner.
     arc_session_runner_ =
         base::MakeUnique<ArcSessionRunner>(base::Bind(FakeArcSession::Create));
@@ skipping 42 matching lines @@
   void OnSessionStopped(ArcStopReason stop_reason, bool restarting) override {
     // The instance is already destructed in
     // ArcSessionRunner::OnSessionStopped().
     stop_reason_ = stop_reason;
     restarting_ = restarting;
   }
 
   ArcStopReason stop_reason_;
   bool restarting_;
   std::unique_ptr<ArcSessionRunner> arc_session_runner_;
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcSessionRunnerTest);
 };
 
 // Exercises the basic functionality of the ArcSessionRunner. Observer should
 // be notified.
 TEST_F(ArcSessionRunnerTest, Basic) {
   class Observer : public ArcSessionRunner::Observer {
    public:
     Observer() = default;
@@ skipping 135 matching lines @@
 
 // Removing an unknown observer should be allowed.
 TEST_F(ArcSessionRunnerTest, RemoveUnknownObserver) {
   EXPECT_TRUE(arc_session_runner()->IsStopped());
 
   DoNothingObserver do_nothing_observer;
   arc_session_runner()->RemoveObserver(&do_nothing_observer);
 }
 
 }  // namespace arc