sketch hooking into PNG_FILTER_OPTIMIZATIONS

src/codec/SkPngFilters.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPngFilters_DEFINED
+#define SkPngFilters_DEFINED
+
+#include "png.h"
+
+// We don't bother specializing Up...
+// it's so simple it's usually already perfectly autovectorized.
+
+// These all require bpp=3 (i.e. RGB).
+void   sk_sub3_sse2(png_row_infop, png_bytep, png_const_bytep);
+void   sk_avg3_sse2(png_row_infop, png_bytep, png_const_bytep);
+void sk_paeth3_sse2(png_row_infop, png_bytep, png_const_bytep);
+
+// These all require bpp=4 (i.e. RGBA).
+void   sk_sub4_sse2(png_row_infop, png_bytep, png_const_bytep);
+void   sk_avg4_sse2(png_row_infop, png_bytep, png_const_bytep);
+void sk_paeth4_sse2(png_row_infop, png_bytep, png_const_bytep);
+
+#endif//SkPngFilterOpts_DEFINED