BUG=156
TEST=./libyuv_unittest --gtest_filter=*ARGBScale*
Review URL: https://webrtc-codereview.appspot.com/930019

git-svn-id: http://libyuv.googlecode.com/svn/trunk@492 16f28f9a-4ce2-e073-06de-1de4eb20be90