BUG=none
TESTED=set LIBYUV_WIDTH=1918 libyuvTest.ScaleDownBy3by4_None
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/47349004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1416 16f28f9a-4ce2-e073-06de-1de4eb20be90