Use ScopedTaskEnvironment instead of MessageLoop in components unit tests.

components/sync/engine_impl/js_mutation_event_observer_unittest.cc

 // Copyright (c) 2012 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/sync/engine_impl/js_mutation_event_observer.h"
 
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/values.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/js/js_event_details.h"
 #include "components/sync/js/js_test_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace syncer {
 namespace {
 
 using ::testing::InSequence;
 using ::testing::StrictMock;
 
 class JsMutationEventObserverTest : public testing::Test {
  protected:
   JsMutationEventObserverTest() {
     js_mutation_event_observer_.SetJsEventHandler(
         mock_js_event_handler_.AsWeakHandle());
   }
 
  private:
   // This must be destroyed after the member variables below in order
   // for WeakHandles to be destroyed properly.
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
  protected:
   StrictMock<MockJsEventHandler> mock_js_event_handler_;
   JsMutationEventObserver js_mutation_event_observer_;
 
   void PumpLoop() { base::RunLoop().RunUntilIdle(); }
 };
 
 TEST_F(JsMutationEventObserverTest, OnChangesApplied) {
   InSequence dummy;
@@ skipping 60 matching lines @@
   }
 
   for (int i = FIRST_REAL_MODEL_TYPE; i < MODEL_TYPE_COUNT; ++i) {
     js_mutation_event_observer_.OnChangesComplete(ModelTypeFromInt(i));
   }
   PumpLoop();
 }
 
 }  // namespace
 }  // namespace syncer