Add the perceptual difference metric to the rebaseline server

gm/rebaseline_server/results.py

Index: gm/rebaseline_server/results.py
diff --git a/gm/rebaseline_server/results.py b/gm/rebaseline_server/results.py
index fff0a941e89aac91d82f390e7e8444eebdcc21b7..3b57bc1e206381cd0066eecbae5983521e5035d1 100755
--- a/gm/rebaseline_server/results.py
+++ b/gm/rebaseline_server/results.py
@@ -432,6 +432,7 @@ class Results(object):
             results_for_this_test['numDifferingPixels'] = 0
             results_for_this_test['percentDifferingPixels'] = 0
             results_for_this_test['weightedDiffMeasure'] = 0
+            results_for_this_test['perceptualDifference'] = 0
             results_for_this_test['maxDiffPerChannel'] = 0
           else:
             try:
@@ -444,6 +445,8 @@ class Results(object):
                   diff_record.get_percent_pixels_differing())
               results_for_this_test['weightedDiffMeasure'] = (
                   diff_record.get_weighted_diff_measure())
+              results_for_this_test['perceptualDifference'] = (
+                  diff_record.get_perceptual_difference())
               results_for_this_test['maxDiffPerChannel'] = (
                   diff_record.get_max_diff_per_channel())
             except KeyError: