Add the perceptual difference metric to the rebaseline server

* Finds the location of the skpdiff binary.
* Calculates the perceptual difference percentage using the skpdiff binary (treats -1 as 0% perceptual similarity).
* Replaces the weightedDiffMeasure in view.html with perceptualDifferent.

BUG=skia:2019
NOTRY=true

Committed: http://code.google.com/p/skia/source/detail?r=13398

R=epoger@google.com

Author: rmistry@google.com

Review URL: https://codereview.chromium.org/147453003

git-svn-id: http://skia.googlecode.com/svn/trunk@13410 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed