Use ScopedTaskEnvironment instead of MessageLoop in content unit tests.

content/renderer/media/android/stream_texture_wrapper_impl_unittest.cc

 // Copyright 2016 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 "content/renderer/media/android/stream_texture_wrapper_impl.h"
 
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace content {
 
 class StreamTextureWrapperImplTest : public testing::Test {
  public:
   StreamTextureWrapperImplTest() {}
 
   // Necessary, or else base::ThreadTaskRunnerHandle::Get() fails.
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(StreamTextureWrapperImplTest);
 };
 
 // This test's purpose is to make sure the StreamTextureWrapperImpl can properly
 // be destroyed via StreamTextureWrapper::Deleter.
 TEST_F(StreamTextureWrapperImplTest, ConstructionDestruction_ShouldSucceed) {
   media::ScopedStreamTextureWrapper stream_texture_wrapper =
       StreamTextureWrapperImpl::Create(false, nullptr,
                                        base::ThreadTaskRunnerHandle::Get());
 }
 
 }  // Content