media: Fix mojo pipeline integration tests.

media/base/null_video_sink.h

Index: media/base/null_video_sink.h
diff --git a/media/base/null_video_sink.h b/media/base/null_video_sink.h
index 66ff79f59f9d2233c9d85d6cdac2665ed567c2a9..b5a384b5bed26c44bf8f5d1467fb7a8a2de4189c 100644
--- a/media/base/null_video_sink.h
+++ b/media/base/null_video_sink.h
@@ -9,6 +9,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/tick_clock.h"
+#include "media/base/media_export.h"
 #include "media/base/video_renderer_sink.h"
 
 namespace base {
@@ -17,7 +18,7 @@ class SingleThreadTaskRunner;
 
 namespace media {
 
-class NullVideoSink : public VideoRendererSink {
+class MEDIA_EXPORT NullVideoSink : public VideoRendererSink {
  public:
   using NewFrameCB = base::Callback<void(const scoped_refptr<VideoFrame>&)>;