When was SkPDiff last used?

tools/skpdiff/SkPMetric.h

-/*
- * 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