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

third_party/libpng/pngusr.h

 /* ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
  * The contents of this file are subject to the Mozilla Public License Version
  * 1.1 (the "License"); you may not use this file except in compliance with
  * the License. You may obtain a copy of the License at
  * http://www.mozilla.org/MPL/
  *
  * Software distributed under the License is distributed on an "AS IS" basis,
  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
@@ skipping 79 matching lines @@
 #define PNG_NO_WRITE_gAMA
 #define PNG_NO_WRITE_hIST
 #define PNG_NO_WRITE_iCCP
 #define PNG_NO_WRITE_oFFs
 #define PNG_NO_WRITE_pCAL
 #define PNG_NO_WRITE_pHYs
 #define PNG_NO_WRITE_sBIT
 #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
 #define PNG_NO_WRITE_EMPTY_PLTE
 #define PNG_NO_WRITE_OPT_PLTE
 #else
 #define PNG_NO_WRITE_SUPPORTED
 #endif
 
 #define PNG_NO_USER_MEM
@@ skipping 373 matching lines @@
 #define png_write_sig                   wk_png_write_sig
 #define png_write_start_row             wk_png_write_start_row
 #define png_write_tEXt                  wk_png_write_tEXt
 #define png_write_tIME                  wk_png_write_tIME
 #define png_write_tRNS                  wk_png_write_tRNS
 #define png_write_zTXt                  wk_png_write_zTXt
 #define png_zalloc                      wk_png_zalloc
 #define png_zfree                       wk_png_zfree
 
 #endif  // CHROME_THIRD_PARTY_LIBPNG_PNGUSR_H__