Revert of Remove unused (by clients) SkUnitMapper (https://codereview.chromium.org/283273002/)

include/core/SkUnitMapper.h

+
+/*
+ * Copyright 2006 The Android Open Source Project
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#ifndef SkUnitMapper_DEFINED
+#define SkUnitMapper_DEFINED
+
+#include "SkRefCnt.h"
+#include "SkScalar.h"
+
+#include "SkFlattenable.h"
+
+class SkUnitMapper : public SkFlattenable {
+public:
+    SK_DECLARE_INST_COUNT(SkUnitMapper)
+
+    SkUnitMapper() {}
+
+    /** Given a value in [0..0xFFFF], return a value in the same range.
+    */
+    virtual uint16_t mapUnit16(uint16_t x) = 0;
+
+    SK_DEFINE_FLATTENABLE_TYPE(SkUnitMapper)
+
+protected:
+    SkUnitMapper(SkReadBuffer& rb) : SkFlattenable(rb) {}
+
+private:
+    typedef SkFlattenable INHERITED;
+};
+
+#endif