Add the ability to write comments to PNGCodec::Encode.

I'm going to use this to write layout test checksums to the
expected png files.

Review URL: http://codereview.chromium.org/6696085

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@79592 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 211 insertions, 50 deletions

diff --git a/chrome/browser/ui/window_snapshot/window_snapshot_win.cc b/chrome/browser/ui/window_snapshot/window_snapshot_win.cc
index b4fcdba..0885c7b 100644
--- a/chrome/browser/ui/window_snapshot/window_snapshot_win.cc
+++ b/chrome/browser/ui/window_snapshot/window_snapshot_win.cc
@@ -9,6 +9,7 @@
 #include "ui/gfx/codec/png_codec.h"
 #include "ui/gfx/gdi_util.h"
 #include "ui/gfx/rect.h"
+#include "ui/gfx/size.h"
 
 namespace browser {
 
@@ -61,7 +62,8 @@ gfx::Rect GrabWindowSnapshot(gfx::NativeWindow window_handle,
   // encode it into a useful format for posting to the bug report
   // server.
   gfx::PNGCodec::Encode(bit_ptr, gfx::PNGCodec::FORMAT_BGRA,
-                        width, height, width * 4, true,
+                        gfx::Size(width, height), width * 4, true,
+                        std::vector<gfx::PNGCodec::Comment>(),
                         png_representation);
 
   ReleaseDC(window_handle, window_hdc);
diff --git a/printing/image.cc b/printing/image.cc
index 5c5213f..a7ae67d 100644
--- a/printing/image.cc
+++ b/printing/image.cc
@@ -60,10 +60,10 @@ bool Image::SaveToPng(const FilePath& filepath) const {
   std::vector<unsigned char> compressed;
   bool success = gfx::PNGCodec::Encode(&*data_.begin(),
                                        gfx::PNGCodec::FORMAT_BGRA,
-                                       size_.width(),
-                                       size_.height(),
+                                       size_,
                                        row_length_,
                                        true,
+                                       std::vector<gfx::PNGCodec::Comment>(),
                                        &compressed);
   DCHECK(success && compressed.size());
   if (success) {
diff --git a/skia/ext/image_operations_unittest.cc b/skia/ext/image_operations_unittest.cc
index c1bd3e1..e8c0e9f 100644
--- a/skia/ext/image_operations_unittest.cc
+++ b/skia/ext/image_operations_unittest.cc
@@ -14,6 +14,7 @@
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkRect.h"
 #include "ui/gfx/codec/png_codec.h"
+#include "ui/gfx/size.h"
 
 namespace {
 
@@ -193,9 +194,9 @@ void SaveBitmapToPNG(const SkBitmap& bmp, const char* path) {
   gfx::PNGCodec::ColorFormat color_format = gfx::PNGCodec::FORMAT_RGBA;
   if (!gfx::PNGCodec::Encode(
           reinterpret_cast<const unsigned char*>(bmp.getPixels()),
-          color_format, bmp.width(), bmp.height(),
+          color_format, gfx::Size(bmp.width(), bmp.height()),
           static_cast<int>(bmp.rowBytes()),
-          false, &png)) {
+          false, std::vector<gfx::PNGCodec::Comment>(), &png)) {
     FAIL() << "Failed to encode image";
   }
 
diff --git a/skia/ext/vector_canvas_unittest.cc b/skia/ext/vector_canvas_unittest.cc
index 1066c0c..355aa13 100644
--- a/skia/ext/vector_canvas_unittest.cc
+++ b/skia/ext/vector_canvas_unittest.cc
@@ -18,6 +18,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/effects/SkDashPathEffect.h"
 #include "ui/gfx/codec/png_codec.h"
+#include "ui/gfx/size.h"
 
 namespace skia {
 
@@ -126,10 +127,10 @@ class Image {
     std::vector<unsigned char> compressed;
     ASSERT_TRUE(gfx::PNGCodec::Encode(&*data_.begin(),
                                       gfx::PNGCodec::FORMAT_BGRA,
-                                      width_,
-                                      height_,
+                                      gfx::Size(width_, height_),
                                       row_length_,
                                       true,
+                                      std::vector<gfx::PNGCodec::Comment>(),
                                       &compressed));
     ASSERT_TRUE(compressed.size());
     FILE* f = file_util::OpenFile(filename, "wb");
diff --git a/third_party/libpng/pngusr.h b/third_party/libpng/pngusr.h
index 04415b1..f2446e1 100644
--- a/third_party/libpng/pngusr.h
+++ b/third_party/libpng/pngusr.h
@@ -97,7 +97,6 @@
 #define PNG_NO_WRITE_sCAL
 #define PNG_NO_WRITE_sPLT
 #define PNG_NO_WRITE_sRGB
-#define PNG_NO_WRITE_TEXT
 #define PNG_NO_WRITE_tIME
 #define PNG_NO_WRITE_UNKNOWN_CHUNKS
 #define PNG_NO_WRITE_USER_CHUNKS
diff --git a/tools/imagediff/DEPS b/tools/imagediff/DEPS
index 1a45e54..b273ae3 100644
--- a/tools/imagediff/DEPS
+++ b/tools/imagediff/DEPS
@@ -1,3 +1,3 @@
 include_rules = [
-  "+ui/gfx/codec",
+  "+ui/gfx",
 ]
diff --git a/tools/imagediff/image_diff.cc b/tools/imagediff/image_diff.cc
index 6f775a5..294e2e3 100644
--- a/tools/imagediff/image_diff.cc
+++ b/tools/imagediff/image_diff.cc
@@ -23,6 +23,7 @@
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
 #include "ui/gfx/codec/png_codec.h"
+#include "ui/gfx/size.h"
 
 #if defined(OS_WIN)
 #include "windows.h"
@@ -316,8 +317,9 @@ int DiffImages(const FilePath& file1, const FilePath& file2,
 
   std::vector<unsigned char> png_encoding;
   gfx::PNGCodec::Encode(diff_image.data(), gfx::PNGCodec::FORMAT_RGBA,
-                        diff_image.w(), diff_image.h(), diff_image.w() * 4,
-                        false, &png_encoding);
+                        gfx::Size(diff_image.w(), diff_image.h()),
+                        diff_image.w() * 4, false,
+                        std::vector<gfx::PNGCodec::Comment>(), &png_encoding);
   if (file_util::WriteFile(out_file,
       reinterpret_cast<char*>(&png_encoding.front()), png_encoding.size()) < 0)
     return kStatusError;
diff --git a/ui/gfx/codec/png_codec.cc b/ui/gfx/codec/png_codec.cc
index 6cd761f..0d9596e 100644
--- a/ui/gfx/codec/png_codec.cc
+++ b/ui/gfx/codec/png_codec.cc
@@ -6,6 +6,8 @@
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/string_util.h"
+#include "ui/gfx/size.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkUnPreMultiply.h"
 #include "third_party/skia/include/core/SkColorPriv.h"
@@ -546,6 +548,58 @@ void ConvertBGRAtoRGB(const unsigned char* bgra, int pixel_width,
   }
 }
 
+#ifdef PNG_TEXT_SUPPORTED
+class CommentWriter {
+ public:
+  explicit CommentWriter(const std::vector<PNGCodec::Comment>& comments)
+      : comments_(comments),
+        png_text_(new png_text[comments.size()]) {
+    for (size_t i = 0; i < comments.size(); ++i)
+      AddComment(i, comments[i]);
+  }
+
+  ~CommentWriter() {
+    for (size_t i = 0; i < comments_.size(); ++i) {
+      free(png_text_[i].key);
+      free(png_text_[i].text);
+    }
+    delete [] png_text_;
+  }
+
+  bool HasComments() {
+    return !comments_.empty();
+  }
+
+  png_text* get_png_text() {
+    return png_text_;
+  }
+
+  int size() {
+    return static_cast<int>(comments_.size());
+  }
+
+ private:
+  void AddComment(size_t pos, const PNGCodec::Comment& comment) {
+    png_text_[pos].compression = PNG_TEXT_COMPRESSION_NONE;
+    // A PNG comment's key can only be 79 characters long.
+    DCHECK(comment.key.length() < 79);
+    png_text_[pos].key = base::strdup(comment.key.substr(0, 78).c_str());
+    png_text_[pos].text = base::strdup(comment.text.c_str());
+    png_text_[pos].text_length = comment.text.length();
+#ifdef PNG_iTXt_SUPPORTED
+    png_text_[pos].itxt_length = 0;
+    png_text_[pos].lang = 0;
+    png_text_[pos].lang_key = 0;
+#endif
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(CommentWriter);
+
+  const std::vector<PNGCodec::Comment> comments_;
+  png_text* png_text_;
+};
+#endif  // PNG_TEXT_SUPPORTED
+
 // The type of functions usable for converting between pixel formats.
 typedef void (*FormatConverter)(const unsigned char* in, int w,
                                 unsigned char* out, bool* is_opaque);
@@ -559,7 +613,8 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
                    int width, int height, int row_byte_width,
                    const unsigned char* input,
                    int png_output_color_type, int output_color_components,
-                   FormatConverter converter) {
+                   FormatConverter converter,
+                   const std::vector<PNGCodec::Comment>& comments) {
   // Make sure to not declare any locals here -- locals in the presence
   // of setjmp() in C++ code makes gcc complain.
 
@@ -572,6 +627,15 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
   png_set_IHDR(png_ptr, info_ptr, width, height, 8, png_output_color_type,
                PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
                PNG_FILTER_TYPE_DEFAULT);
+
+#ifdef PNG_TEXT_SUPPORTED
+  CommentWriter comment_writer(comments);
+  if (comment_writer.HasComments()) {
+    png_set_text(png_ptr, info_ptr, comment_writer.get_png_text(),
+                 comment_writer.size());
+  }
+#endif
+
   png_write_info(png_ptr, info_ptr);
 
   if (!converter) {
@@ -598,8 +662,9 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
 
 // static
 bool PNGCodec::Encode(const unsigned char* input, ColorFormat format,
-                      int w, int h, int row_byte_width,
+                      const Size& size, int row_byte_width,
                       bool discard_transparency,
+                      const std::vector<Comment>& comments,
                       std::vector<unsigned char>* output) {
   // Run to convert an input row into the output row format, NULL means no
   // conversion is necessary.
@@ -660,7 +725,7 @@ bool PNGCodec::Encode(const unsigned char* input, ColorFormat format,
   }
 
   // Row stride should be at least as long as the length of the data.
-  DCHECK(input_color_components * w <= row_byte_width);
+  DCHECK(input_color_components * size.width() <= row_byte_width);
 
   png_struct* png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
                                                 NULL, NULL, NULL);
@@ -674,9 +739,9 @@ bool PNGCodec::Encode(const unsigned char* input, ColorFormat format,
 
   PngEncoderState state(output);
   bool success = DoLibpngWrite(png_ptr, info_ptr, &state,
-                               w, h, row_byte_width, input,
-                               png_output_color_type, output_color_components,
-                               converter);
+                               size.width(), size.height(), row_byte_width,
+                               input, png_output_color_type,
+                               output_color_components, converter, comments);
   png_destroy_write_struct(&png_ptr, &info_ptr);
 
   return success;
@@ -692,8 +757,16 @@ bool PNGCodec::EncodeBGRASkBitmap(const SkBitmap& input,
   DCHECK(input.empty() || input.bytesPerPixel() == bbp);
 
   return Encode(reinterpret_cast<unsigned char*>(input.getAddr32(0, 0)),
-                FORMAT_SkBitmap, input.width(), input.height(),
-                input.width() * bbp, discard_transparency, output);
+                FORMAT_SkBitmap, Size(input.width(), input.height()),
+                input.width() * bbp, discard_transparency,
+                std::vector<Comment>(), output);
+}
+
+PNGCodec::Comment::Comment(const std::string& k, const std::string& t)
+    : key(k), text(t) {
+}
+
+PNGCodec::Comment::~Comment() {
 }
 
 }  // namespace gfx
diff --git a/ui/gfx/codec/png_codec.h b/ui/gfx/codec/png_codec.h
index 73453fe..eac411d 100644
--- a/ui/gfx/codec/png_codec.h
+++ b/ui/gfx/codec/png_codec.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -6,6 +6,7 @@
 #define UI_GFX_CODEC_PNG_CODEC_H_
 #pragma once
 
+#include <string>
 #include <vector>
 
 #include "base/basictypes.h"
@@ -14,6 +15,8 @@ class SkBitmap;
 
 namespace gfx {
 
+class Size;
+
 // Interface for encoding and decoding PNG data. This is a wrapper around
 // libpng, which has an inconvenient interface for callers. This is currently
 // designed for use in tests only (where we control the files), so the handling
@@ -39,6 +42,15 @@ class PNGCodec {
     FORMAT_SkBitmap
   };
 
+  // Represents a comment in the tEXt ancillary chunk of the png.
+  struct Comment {
+    Comment(const std::string& k, const std::string& t);
+    ~Comment();
+
+    std::string key;
+    std::string text;
+  };
+
   // Encodes the given raw 'input' data, with each pixel being represented as
   // given in 'format'. The encoded PNG data will be written into the supplied
   // vector and true will be returned on success. On failure (false), the
@@ -47,7 +59,7 @@ class PNGCodec {
   // When writing alpha values, the input colors are assumed to be post
   // multiplied.
   //
-  // w, h: dimensions of the image
+  // size: dimensions of the image
   // row_byte_width: the width in bytes of each row. This may be greater than
   //   w * bytes_per_pixel if there is extra padding at the end of each row
   //   (often, each row is padded to the next machine word).
@@ -55,9 +67,13 @@ class PNGCodec {
   //   alpha values, these alpha values will be discarded and only RGB will be
   //   written to the resulting file. Otherwise, alpha values in the input
   //   will be preserved.
-  static bool Encode(const unsigned char* input, ColorFormat format,
-                     int w, int h, int row_byte_width,
+  // comments: comments to be written in the png's metadata.
+  static bool Encode(const unsigned char* input,
+                     ColorFormat format,
+                     const Size& size,
+                     int row_byte_width,
                      bool discard_transparency,
+                     const std::vector<Comment>& comments,
                      std::vector<unsigned char>* output);
 
   // Call PNGCodec::Encode on the supplied SkBitmap |input|, which is assumed
diff --git a/ui/gfx/codec/png_codec_unittest.cc b/ui/gfx/codec/png_codec_unittest.cc
index 72ed671..b31dbd2 100644
--- a/ui/gfx/codec/png_codec_unittest.cc
+++ b/ui/gfx/codec/png_codec_unittest.cc
@@ -1,13 +1,15 @@
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
-#include <math.h>
+#include <algorithm>
+#include <cmath>
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkUnPreMultiply.h"
 #include "ui/gfx/codec/png_codec.h"
+#include "ui/gfx/size.h"
 
 namespace gfx {
 
@@ -79,8 +81,10 @@ TEST(PNGCodec, EncodeDecodeRGB) {
 
   // encode
   std::vector<unsigned char> encoded;
-  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGB, w, h,
-                               w * 3, false, &encoded));
+  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGB,
+                               Size(w, h), w * 3, false,
+                               std::vector<PNGCodec::Comment>(),
+                               &encoded));
 
   // decode, it should have the same size as the original
   std::vector<unsigned char> decoded;
@@ -106,8 +110,10 @@ TEST(PNGCodec, EncodeDecodeRGBA) {
 
   // encode
   std::vector<unsigned char> encoded;
-  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGBA, w, h,
-                               w * 4, false, &encoded));
+  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGBA,
+                               Size(w, h), w * 4, false,
+                               std::vector<PNGCodec::Comment>(),
+                               &encoded));
 
   // decode, it should have the same size as the original
   std::vector<unsigned char> decoded;
@@ -140,8 +146,10 @@ TEST(PNGCodec, DecodeCorrupted) {
 
   // Make some compressed data.
   std::vector<unsigned char> compressed;
-  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGB, w, h,
-                               w * 3, false, &compressed));
+  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGB,
+                               Size(w, h), w * 3, false,
+                               std::vector<PNGCodec::Comment>(),
+                               &compressed));
 
   // Try decompressing a truncated version.
   EXPECT_FALSE(PNGCodec::Decode(&compressed[0], compressed.size() / 2,
@@ -166,8 +174,10 @@ TEST(PNGCodec, EncodeDecodeBGRA) {
 
   // Encode.
   std::vector<unsigned char> encoded;
-  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_BGRA, w, h,
-                               w * 4, false, &encoded));
+  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_BGRA,
+                               Size(w, h), w * 4, false,
+                               std::vector<PNGCodec::Comment>(),
+                               &encoded));
 
   // Decode, it should have the same size as the original.
   std::vector<unsigned char> decoded;
@@ -194,10 +204,10 @@ TEST(PNGCodec, StripAddAlpha) {
 
   // Encode RGBA data as RGB.
   std::vector<unsigned char> encoded;
-  EXPECT_TRUE(PNGCodec::Encode(&original_rgba[0],
-                               PNGCodec::FORMAT_RGBA,
-                               w, h,
-                               w * 4, true, &encoded));
+  EXPECT_TRUE(PNGCodec::Encode(&original_rgba[0], PNGCodec::FORMAT_RGBA,
+                               Size(w, h), w * 4, true,
+                               std::vector<PNGCodec::Comment>(),
+                               &encoded));
 
   // Decode the RGB to RGBA.
   std::vector<unsigned char> decoded;
@@ -213,10 +223,10 @@ TEST(PNGCodec, StripAddAlpha) {
   ASSERT_TRUE(original_rgba == decoded);
 
   // Encode RGBA to RGBA.
-  EXPECT_TRUE(PNGCodec::Encode(&original_rgba[0],
-                               PNGCodec::FORMAT_RGBA,
-                               w, h,
-                               w * 4, false, &encoded));
+  EXPECT_TRUE(PNGCodec::Encode(&original_rgba[0], PNGCodec::FORMAT_RGBA,
+                               Size(w, h), w * 4, false,
+                               std::vector<PNGCodec::Comment>(),
+                               &encoded));
 
   // Decode the RGBA to RGB.
   EXPECT_TRUE(PNGCodec::Decode(&encoded[0], encoded.size(),
@@ -294,4 +304,39 @@ TEST(PNGCodec, EncodeBGRASkBitmapDiscardTransparency) {
   }
 }
 
+TEST(PNGCodec, EncodeWithComment) {
+  const int w = 10, h = 10;
+
+  std::vector<unsigned char> original;
+  MakeRGBImage(w, h, &original);
+
+  std::vector<unsigned char> encoded;
+  std::vector<PNGCodec::Comment> comments;
+  comments.push_back(PNGCodec::Comment("key", "text"));
+  comments.push_back(PNGCodec::Comment("test", "something"));
+  comments.push_back(PNGCodec::Comment("have some", "spaces in both"));
+  EXPECT_TRUE(PNGCodec::Encode(&original[0], PNGCodec::FORMAT_RGB,
+                               Size(w, h), w * 3, false, comments, &encoded));
+
+  // Each chunk is of the form length (4 bytes), chunk type (tEXt), data,
+  // checksum (4 bytes).  Make sure we find all of them in the encoded
+  // results.
+  const unsigned char kExpected1[] =
+      "\x00\x00\x00\x08tEXtkey\x00text\x9e\xe7\x66\x51";
+  const unsigned char kExpected2[] =
+      "\x00\x00\x00\x0etEXttest\x00something\x29\xba\xef\xac";
+  const unsigned char kExpected3[] =
+      "\x00\x00\x00\x18tEXthave some\x00spaces in both\x8d\x69\x34\x2d";
+
+  EXPECT_NE(search(encoded.begin(), encoded.end(), kExpected1,
+                   kExpected1 + arraysize(kExpected1)),
+            encoded.end());
+  EXPECT_NE(search(encoded.begin(), encoded.end(), kExpected2,
+                   kExpected2 + arraysize(kExpected2)),
+            encoded.end());
+  EXPECT_NE(search(encoded.begin(), encoded.end(), kExpected3,
+                   kExpected3 + arraysize(kExpected3)),
+            encoded.end());
+}
+
 }  // namespace gfx
diff --git a/webkit/support/webkit_support_gfx.h b/webkit/support/webkit_support_gfx.h
index 60bb765..e652d1c 100644
--- a/webkit/support/webkit_support_gfx.h
+++ b/webkit/support/webkit_support_gfx.h
@@ -1,13 +1,15 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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 WEBKIT_SUPPORT_WEBKIT_SUPPORT_GFX_H_
 #define WEBKIT_SUPPORT_WEBKIT_SUPPORT_GFX_H_
 
+#include <string>
 #include <vector>
 
 #include "ui/gfx/codec/png_codec.h"
+#include "ui/gfx/size.h"
 
 namespace webkit_support {
 
@@ -20,20 +22,40 @@ inline bool DecodePNG(const unsigned char* input, size_t input_size,
 }
 
 // Encode an RGBA pixel array into a PNG.
-inline bool EncodeRGBAPNG(const unsigned char* input, int width, int height,
+inline bool EncodeRGBAPNG(const unsigned char* input,
+                          int width,
+                          int height,
                           int row_byte_width,
                           std::vector<unsigned char>* output) {
-  return gfx::PNGCodec::Encode(input, gfx::PNGCodec::FORMAT_RGBA, width,
-                               height, row_byte_width, false, output);
+  return gfx::PNGCodec::Encode(input, gfx::PNGCodec::FORMAT_RGBA,
+      gfx::Size(width, height), row_byte_width, false,
+      std::vector<gfx::PNGCodec::Comment>(), output);
 }
 
 // Encode an BGRA pixel array into a PNG.
-inline bool EncodeBGRAPNG(const unsigned char* input, int width, int height,
-                          int row_byte_width, bool discard_transparency,
+inline bool EncodeBGRAPNG(const unsigned char* input,
+                          int width,
+                          int height,
+                          int row_byte_width,
+                          bool discard_transparency,
+                          std::vector<unsigned char>* output) {
+  return gfx::PNGCodec::Encode(input, gfx::PNGCodec::FORMAT_BGRA,
+      gfx::Size(width, height), row_byte_width, discard_transparency,
+      std::vector<gfx::PNGCodec::Comment>(), output);
+}
+
+inline bool EncodeBGRAPNGWithChecksum(const unsigned char* input,
+                          int width,
+                          int height,
+                          int row_byte_width,
+                          bool discard_transparency,
+                          const std::string& checksum,
                           std::vector<unsigned char>* output) {
-  return gfx::PNGCodec::Encode(input, gfx::PNGCodec::FORMAT_BGRA, width,
-                               height, row_byte_width, discard_transparency,
-                               output);
+  std::vector<gfx::PNGCodec::Comment> comments;
+  comments.push_back(gfx::PNGCodec::Comment("checksum", checksum));
+  return gfx::PNGCodec::Encode(input, gfx::PNGCodec::FORMAT_BGRA,
+      gfx::Size(width, height), row_byte_width, discard_transparency,
+      comments, output);
 }
 
 }  // namespace webkit_support