add test for box filter before improving odd width. BUG=431 TESTED=ARGBScaleDownBy4_Box
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: a51711482b6ba0e1d1ab095578a045eeae45ac9a@1411 16f28f9a-4ce2-e073-06de-1de4eb20be90

rig-project/libyuv,rig-project/libyuv,rig-project/libyuv