add diff viewer website

experimental/skpdiff/SkPMetric.cpp

 #include <cmath>
 
 #include "SkBitmap.h"
 #include "skpdiff_util.h"
 #include "SkPMetric.h"
 
 struct RGB {
     float r, g, b;
 };
 
@@ skipping 361 matching lines @@
             if (isFailure) {
                 failures++;
                 poi->push()->set(x, y);
             }
         }
     }
 
     SkDELETE_ARRAY(cyclesPerDegree);
     SkDELETE_ARRAY(contrast);
     SkDELETE_ARRAY(thresholdFactorFrequency);
-    return (double)failures;
+    return 1.0 - (double)failures / (width * height);
 }
 
 const char* SkPMetric::getName() {
     return "perceptual";
 }
 
 int SkPMetric::queueDiff(SkBitmap* baseline, SkBitmap* test) {
     int diffID = fQueuedDiffs.count();
     double startTime = get_seconds();
     QueuedDiff& diff = fQueuedDiffs.push_back();
@@ skipping 32 matching lines @@
     return fQueuedDiffs[id].result;
 }
 
 int SkPMetric::getPointsOfInterestCount(int id) {
     return fQueuedDiffs[id].poi.count();
 }
 
 SkIPoint* SkPMetric::getPointsOfInterest(int id) {
     return fQueuedDiffs[id].poi.begin();
 }