URL: http://www.libpng.org/pub/png/libpng.html
Version: 1.6.16
License: libpng license
License File: LICENSE, pulled out of png.h
Description: png compression/decompression library
Local Modifications: (1) Created pnglibconf.h from pnglibconf.h.prebuilt (a
    rename with a few additional settings enabled). (2) Created pngprefix.h
    that is required when using the PNG_PREFIX define. (3) Pulled LICENSE into
    its own file.

FAQ:
Q: Why does this directory exist?
A: libpng is pulled in through DEPS, but in order to build it using ninja, we
   need to create pnglibconf.h and pngprefix.h.  We originally tried creating
   the file as an action in https://codereview.chromium.org/930283002/, but this
   apparently led to a race condition on Windows, where some builds failed to
   create the file in time for other files to include it. By checking these
   files directly into Skia, we eliminate the race condition.