When was SkPDiff last used?

tools/skpdiff/SkPMetric.h

Index: tools/skpdiff/SkPMetric.h
diff --git a/tools/skpdiff/SkPMetric.h b/tools/skpdiff/SkPMetric.h
deleted file mode 100644
index 0448708980170b36ac25937bebd8de5ef686f187..0000000000000000000000000000000000000000
--- a/tools/skpdiff/SkPMetric.h
+++ /dev/null
@@ -1,30 +0,0 @@
-/*
- * Copyright 2013 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkPMetric_DEFINED
-#define SkPMetric_DEFINED
-
-#include "SkTArray.h"
-#include "SkTDArray.h"
-
-#include "SkImageDiffer.h"
-
-/**
- * An image differ that uses the pdiff image metric to compare images.
- */
-class SkPMetric : public SkImageDiffer {
-public:
-    const char* getName() const override { return "perceptual"; }
-    virtual bool diff(SkBitmap* baseline, SkBitmap* test, const BitmapsToCreate& bitmapsToCreate,
-                      Result* result) const override;
-
-private:
-    typedef SkImageDiffer INHERITED;
-};
-
-
-#endif