BUG=334
TESTED=unittests added to test functionality that is reversible.
R=sandersd@chromium.org

Review URL: https://webrtc-codereview.appspot.com/15679004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1009 16f28f9a-4ce2-e073-06de-1de4eb20be90