Add "score" unit to SSIM perf score output.

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
diff --git a/webrtc/tools/frame_analyzer/video_quality_analysis.cc b/webrtc/tools/frame_analyzer/video_quality_analysis.cc
index c2a5e49..f5608c8 100644
--- a/webrtc/tools/frame_analyzer/video_quality_analysis.cc
+++ b/webrtc/tools/frame_analyzer/video_quality_analysis.cc
@@ -356,7 +356,7 @@
          ++iter) {
       fprintf(output, "%f,", iter->ssim_value);
     }
-    fprintf(output, "%f]\n", iter->ssim_value);
+    fprintf(output, "%f] score\n", iter->ssim_value);
   }
 }