1d14e42df7
This restores d9dce2f48eed1368a44c368fa87a506bd89ffec5 Switched to using signed shift-and-narrow. Instead of saturating negative results to 0, it was saturating them to 255. BUG=webm:817 BUG=webm:1273 Change-Id: I571095336aa4182e3288b17924fcaaece42b0a49