Use ScopedTaskEnvironment instead of MessageLoop in content unit tests.

content/renderer/media_capture_from_element/html_audio_element_capturer_source_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_capture_from_element/html_audio_element_capturer_source.h"
 #include "base/memory/weak_ptr.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/public/renderer/media_stream_audio_sink.h"
 #include "content/renderer/media/media_stream_audio_track.h"
-#include "content/renderer/media_capture_from_element/html_audio_element_capturer_source.h"
 #include "media/audio/null_audio_sink.h"
 #include "media/base/audio_parameters.h"
 #include "media/base/fake_audio_render_callback.h"
 #include "media/base/media_log.h"
 #include "media/blink/webaudiosourceprovider_impl.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/WebKit/public/platform/WebString.h"
 #include "third_party/WebKit/public/web/WebHeap.h"
 
@@ skipping 83 matching lines @@
 
   MediaStreamAudioTrack* track() const {
     return MediaStreamAudioTrack::From(blink_audio_track_);
   }
 
   int InjectAudio(media::AudioBus* audio_bus) {
     return audio_source_->RenderForTesting(audio_bus);
   }
 
  protected:
-  const base::MessageLoop message_loop_;
+  const base::test::ScopedTaskEnvironment scoped_task_environment_;
 
   blink::WebMediaStreamSource blink_audio_source_;
   blink::WebMediaStreamTrack blink_audio_track_;
 
   media::FakeAudioRenderCallback fake_callback_;
   scoped_refptr<media::WebAudioSourceProviderImpl> audio_source_;
 };
 
 // Constructs and destructs all objects. This is a non trivial sequence.
 TEST_F(HTMLAudioElementCapturerSourceTest, ConstructAndDestruct) {
@@ skipping 22 matching lines @@
   std::unique_ptr<media::AudioBus> bus = media::AudioBus::Create(
       kNumChannelsForTest, kAudioTrackSamplesPerBuffer);
   InjectAudio(bus.get());
   run_loop.Run();
 
   track()->Stop();
   track()->RemoveSink(&sink);
 }
 
 }  // namespace content