Tweak libpng encoding parameters to increase speed on very large images.

ui/gfx/codec/png_codec.h

 // 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 UI_GFX_CODEC_PNG_CODEC_H_
 #define UI_GFX_CODEC_PNG_CODEC_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 78 matching lines @@
                                  bool discard_transparency,
                                  std::vector<unsigned char>* output);
 
   // Call PNGCodec::Encode on the supplied SkBitmap |input|. The difference
   // between this and the previous method is that this restricts compression to
   // zlib q1, which is just rle encoding.
   static bool FastEncodeBGRASkBitmap(const SkBitmap& input,
                                      bool discard_transparency,
                                      std::vector<unsigned char>* output);
 
+  // Similar to FastEncodeBGRASkBitmap, but with no compression at all.
+  static bool NoCompressEncodeBGRASkBitmap(const SkBitmap& input,
+                                           bool discard_transparency,
+                                           std::vector<unsigned char>* output);
+
   // Call PNGCodec::Encode on the supplied SkBitmap |input|, which is assumed
   // to be kA8_Config, 8 bits per pixel. The bitmap is encoded as a grayscale
   // PNG with alpha used for color intensity. The |output| param is passed
   // directly to Encode; refer to Encode for more information. During the call,
   // an SkAutoLockPixels lock is held on |input|.
   static bool EncodeA8SkBitmap(const SkBitmap& input,
                                std::vector<unsigned char>* output);
 
   // Decodes the PNG data contained in input of length input_size. The
   // decoded data will be placed in *output with the dimensions in *w and *h
@@ skipping 18 matching lines @@
   static bool Decode(const unsigned char* input, size_t input_size,
                      SkBitmap* bitmap);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PNGCodec);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_CODEC_PNG_CODEC_H_