BUG=314
TESTED=out\release\libyuv_unittest --gtest_filter=*.ScaleDownBy4*

Review URL: https://webrtc-codereview.appspot.com/46159004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1390 16f28f9a-4ce2-e073-06de-1de4eb20be90