rebaseline_server: use just skpdiff, not Python Image Library

BUG=skia:2414
R=djsollen@google.com, borenet@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/325413003
diff --git a/tools/skpdiff/SkPMetric.h b/tools/skpdiff/SkPMetric.h
index b60858a..00a3d7a 100644
--- a/tools/skpdiff/SkPMetric.h
+++ b/tools/skpdiff/SkPMetric.h
@@ -19,7 +19,7 @@
 class SkPMetric : public SkImageDiffer {
 public:
     virtual const char* getName() const SK_OVERRIDE { return "perceptual"; }
-    virtual bool diff(SkBitmap* baseline, SkBitmap* test, bool computeMask,
+    virtual bool diff(SkBitmap* baseline, SkBitmap* test, const BitmapsToCreate& bitmapsToCreate,
                       Result* result) const SK_OVERRIDE;
 
 private: