Currently, the SSIM values don't have a unit, which makes them default to lower being better rather than the opposite (which is the case for SSIM). R=phoglund@webrtc.org BUG= Review URL: https://webrtc-codereview.appspot.com/41709004 Cr-Commit-Position: refs/heads/master@{#8183} git-svn-id: http://webrtc.googlecode.com/svn/trunk@8183 4adac7df-926f-26a2-2b94-8c16560cd09d