add test for box filter before improving odd width.
BUG=431
TESTED=ARGBScaleDownBy4_Box

Review URL: https://webrtc-codereview.appspot.com/57409004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1411 16f28f9a-4ce2-e073-06de-1de4eb20be90
1 file changed