Use ScopedTaskEnvironment instead of MessageLoopForUI in content tests.

content/renderer/media/webrtc/media_stream_track_metrics_unittest.cc

Index: content/renderer/media/webrtc/media_stream_track_metrics_unittest.cc
diff --git a/content/renderer/media/webrtc/media_stream_track_metrics_unittest.cc b/content/renderer/media/webrtc/media_stream_track_metrics_unittest.cc
index 05de51411e64955212c622b3ddd9f04e7b6b3a84..a0afa8ad024411a48b3af606b43c2a7c7194aed8 100644
--- a/content/renderer/media/webrtc/media_stream_track_metrics_unittest.cc
+++ b/content/renderer/media/webrtc/media_stream_track_metrics_unittest.cc
@@ -5,8 +5,8 @@
 #include <stddef.h>
 
 #include "base/bind.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread.h"
 #include "content/renderer/media/webrtc/media_stream_track_metrics.h"
 #include "content/renderer/media/webrtc/mock_peer_connection_dependency_factory.h"
@@ -85,7 +85,11 @@ class MockMediaStreamTrackMetrics : public MediaStreamTrackMetrics {
 
 class MediaStreamTrackMetricsTest : public testing::Test {
  public:
-  MediaStreamTrackMetricsTest() : signaling_thread_("signaling_thread") {}
+  MediaStreamTrackMetricsTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI),
+        signaling_thread_("signaling_thread") {}
+
   void SetUp() override {
     metrics_.reset(new MockMediaStreamTrackMetrics());
     stream_ = new rtc::RefCountedObject<MockMediaStream>("stream");
@@ -146,7 +150,7 @@ class MediaStreamTrackMetricsTest : public testing::Test {
   std::unique_ptr<MockMediaStreamTrackMetrics> metrics_;
   scoped_refptr<MediaStreamInterface> stream_;
 
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   base::Thread signaling_thread_;
 };