BUG=388
TESTED=out\release\libyuv_unittest --gtest_catch_exceptions=0 --gtest_filter=*420ToARGB_Opt  | sortms
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/34609004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1216 16f28f9a-4ce2-e073-06de-1de4eb20be90