Revert "Add image_diff from the chromium repo."

sky/tools/imagediff/image_diff_png.h

Index: sky/tools/imagediff/image_diff_png.h
diff --git a/sky/tools/imagediff/image_diff_png.h b/sky/tools/imagediff/image_diff_png.h
deleted file mode 100644
index c371337f99d30e9c188f70ccb1905ccde35eda78..0000000000000000000000000000000000000000
--- a/sky/tools/imagediff/image_diff_png.h
+++ /dev/null
@@ -1,35 +0,0 @@
-// Copyright 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef TOOLS_IMAGEDIFF_IMAGE_DIFF_PNG_H_
-#define TOOLS_IMAGEDIFF_IMAGE_DIFF_PNG_H_
-
-#include <string>
-#include <vector>
-
-namespace image_diff_png {
-
-// Decode a PNG into an RGBA pixel array.
-bool DecodePNG(const unsigned char* input, size_t input_size,
-               std::vector<unsigned char>* output,
-               int* width, int* height);
-
-// Encode an RGBA pixel array into a PNG.
-bool EncodeRGBAPNG(const unsigned char* input,
-                   int width,
-                   int height,
-                   int row_byte_width,
-                   std::vector<unsigned char>* output);
-
-// Encode an BGRA pixel array into a PNG.
-bool EncodeBGRAPNG(const unsigned char* input,
-                   int width,
-                   int height,
-                   int row_byte_width,
-                   bool discard_transparency,
-                   std::vector<unsigned char>* output);
-
-}  // namespace image_diff_png
-
-#endif  // TOOLS_IMAGEDIFF_IMAGE_DIFF_PNG_H_