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

ui/gfx/codec/png_codec.cc

Index: ui/gfx/codec/png_codec.cc
diff --git a/ui/gfx/codec/png_codec.cc b/ui/gfx/codec/png_codec.cc
index ac386ad91d0b656e146776c8077694c881719e99..5c0b68d7f163c70806ca162588aaba8b221fccf0 100644
--- a/ui/gfx/codec/png_codec.cc
+++ b/ui/gfx/codec/png_codec.cc
@@ -588,6 +588,8 @@ bool DoLibpngWrite(png_struct* png_ptr, png_info* info_ptr,
   }
 
   png_set_compression_level(png_ptr, compression_level);
+  if (compression_level <= Z_BEST_SPEED)

[dcheng, 2016/04/22 01:14:01]

Alternatively, I could add another parameter to DoLibPngWrite and
EncodeWithCompressionLevel. However, I felt like libpng's filter parameters are
kind of opaque and hard to understand, so I just hardcoded here: the idea is if
you are passing Z_BEST_SPEED, you probably want it to be as fast as possible.

+    png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_NO_FILTERS);
 
   // Set our callback for libpng to give us the data.
   png_set_write_fn(png_ptr, state, EncoderWriteCallback, FakeFlushCallback);
@@ -803,6 +805,14 @@ bool PNGCodec::FastEncodeBGRASkBitmap(const SkBitmap& input,
                                 output);
 }
 
+bool PNGCodec::NoCompressEncodeBGRASkBitmap(
+    const SkBitmap& input,
+    bool discard_transparency,
+    std::vector<unsigned char>* output) {
+  return InternalEncodeSkBitmap(input, discard_transparency, Z_NO_COMPRESSION,
+                                output);
+}
+
 PNGCodec::Comment::Comment(const std::string& k, const std::string& t)
     : key(k), text(t) {
 }