Use ScopedTaskEnvironment instead of MessageLoop in components unit tests.

components/prefs/pref_member_unittest.cc

 // Copyright (c) 2011 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 "components/prefs/pref_member.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/testing_pref_service.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
 const char kBoolPref[] = "bool";
 const char kIntPref[] = "int";
 const char kDoublePref[] = "double";
@@ skipping 75 matching lines @@
   StringPrefMember str_;
   int observe_cnt_;
 
  private:
   PrefService* prefs_;
 };
 
 }  // anonymous namespace
 
 class PrefMemberTest : public testing::Test {
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 TEST_F(PrefMemberTest, BasicGetAndSet) {
   TestingPrefServiceSimple prefs;
   RegisterTestPrefs(prefs.registry());
 
   // Test bool
   BooleanPrefMember boolean;
   boolean.Init(kBoolPref, &prefs);
 
@@ skipping 201 matching lines @@
   helper->FetchValue();
   EXPECT_TRUE(helper->value());
 
   helper->Destroy();
 
   helper->FetchValue();
   EXPECT_TRUE(helper->value());
 
   helper->StopThread();
 }