Use ScopedTaskEnvironment instead of MessageLoop in components unit tests.

components/sync/base/weak_handle_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/base/weak_handle.h"
 
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace syncer {
 
 using ::testing::_;
 using ::testing::SaveArg;
 using ::testing::StrictMock;
 
@@ skipping 37 matching lines @@
     t.task_runner()->PostTask(
         from_here, base::Bind(&WeakHandleTest::CallTest, from_here, h));
   }
 
  private:
   static void CallTest(tracked_objects::Location from_here,
                        const WeakHandle<Base>& h) {
     h.Call(from_here, &Base::Test);
   }
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 TEST_F(WeakHandleTest, Uninitialized) {
   // Default.
   WeakHandle<int> h;
   EXPECT_FALSE(h.IsInitialized());
   // Copy.
   {
     WeakHandle<int> h2(h);
     EXPECT_FALSE(h2.IsInitialized());
@@ skipping 231 matching lines @@
   EXPECT_FALSE(base_weak_handle.IsInitialized());
 }
 
 TEST_F(WeakHandleTest, TypeConversionConstructorUninitializedAssignment) {
   WeakHandle<Base> base_weak_handle;
   base_weak_handle = WeakHandle<Derived>();
   EXPECT_FALSE(base_weak_handle.IsInitialized());
 }
 
 }  // namespace syncer