Replace WaitableEvents and ConditionalVariables in VideoRendererBase tests with MessageLoop.

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index 0b991e0808d4f9ba434ef99345a71ce285ca2bbb..86a3d21323f268238e29507fb947bc96fe8d5893 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -795,14 +795,14 @@
         'base/gmock_callback_support.h',
         'base/mock_audio_renderer_sink.cc',
         'base/mock_audio_renderer_sink.h',
-        'base/mock_callback.cc',
-        'base/mock_callback.h',
         'base/mock_data_source_host.cc',
         'base/mock_data_source_host.h',
         'base/mock_demuxer_host.cc',
         'base/mock_demuxer_host.h',
         'base/mock_filters.cc',
         'base/mock_filters.h',
+        'base/test_helpers.cc',
+        'base/test_helpers.h',
       ],
     },
   ],