Added MediaSourceState unit test.

media/blink/video_frame_compositor_unittest.cc

Index: media/blink/video_frame_compositor_unittest.cc
diff --git a/media/blink/video_frame_compositor_unittest.cc b/media/blink/video_frame_compositor_unittest.cc
index c20dab5275370c76edc32c997097a62057333387..e987cb90482005091c9f783f2ba5a959379bb747 100644
--- a/media/blink/video_frame_compositor_unittest.cc
+++ b/media/blink/video_frame_compositor_unittest.cc
@@ -8,6 +8,7 @@
 #include "base/run_loop.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "cc/layers/video_frame_provider.h"
+#include "media/base/gmock_callback_support.h"
 #include "media/base/video_frame.h"
 #include "media/blink/video_frame_compositor.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ -19,10 +20,6 @@ using testing::Return;
 
 namespace media {
 
-ACTION_P(RunClosure, closure) {
-  closure.Run();
-}
-
 class VideoFrameCompositorTest : public testing::Test,
                                  public cc::VideoFrameProvider::Client,
                                  public VideoRendererSink::RenderCallback {