Use ScopedTaskEnvironment instead of MessageLoopForUI in content tests.

content/renderer/media/webrtc/media_stream_remote_video_source_unittest.cc

Index: content/renderer/media/webrtc/media_stream_remote_video_source_unittest.cc
diff --git a/content/renderer/media/webrtc/media_stream_remote_video_source_unittest.cc b/content/renderer/media/webrtc/media_stream_remote_video_source_unittest.cc
index f84331486ec107516e91c1c4d47df40e8e52e810..cc19146a8663aa1d5450c726097af65c300b24cd 100644
--- a/content/renderer/media/webrtc/media_stream_remote_video_source_unittest.cc
+++ b/content/renderer/media/webrtc/media_stream_remote_video_source_unittest.cc
@@ -7,9 +7,9 @@
 #include <memory>
 #include <utility>
 
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/child/child_process.h"
 #include "content/renderer/media/media_stream_video_track.h"
@@ -39,7 +39,9 @@ class MediaStreamRemoteVideoSourceTest
     : public ::testing::Test {
  public:
   MediaStreamRemoteVideoSourceTest()
-      : child_process_(new ChildProcess()),
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI),
+        child_process_(new ChildProcess()),
         mock_factory_(new MockPeerConnectionDependencyFactory()),
         webrtc_video_track_(MockWebRtcVideoTrack::Create("test")),
         remote_source_(new MediaStreamRemoteVideoSourceUnderTest(
@@ -101,7 +103,7 @@ class MediaStreamRemoteVideoSourceTest
       ++number_of_failed_track_starts_;
   }
 
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::unique_ptr<ChildProcess> child_process_;
   std::unique_ptr<MockPeerConnectionDependencyFactory> mock_factory_;
   scoped_refptr<webrtc::VideoTrackInterface> webrtc_video_track_;