Use ScopedTaskEnvironment instead of MessageLoop in media unit tests.

media/remoting/courier_renderer_unittest.cc

Index: media/remoting/courier_renderer_unittest.cc
diff --git a/media/remoting/courier_renderer_unittest.cc b/media/remoting/courier_renderer_unittest.cc
index 524d7beeecf65477b3fc50ea83c1b9672440a1de..1e5606274675a89b85223c99fb09838855e85151 100644
--- a/media/remoting/courier_renderer_unittest.cc
+++ b/media/remoting/courier_renderer_unittest.cc
@@ -6,6 +6,7 @@
 
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "media/base/pipeline_status.h"
@@ -328,7 +329,7 @@ class CourierRendererTest : public testing::Test {
     RunPendingTasks();
   }
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::unique_ptr<RendererController> controller_;
   std::unique_ptr<RendererClientImpl> render_client_;
   std::unique_ptr<FakeMediaResource> media_resource_;