Enable VideoAdapterTest.BlackOutput on DrMemory.

DrMemory r2061 fixes how the instruction psrlw's shadow is mirrored ->
this false positive is now gone.

R=kjellander@webrtc.org
BUG=3754

Review URL: https://webrtc-codereview.appspot.com/25399004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7080 4adac7df-926f-26a2-2b94-8c16560cd09d