anchor.diff:  , bzip2, flac, speex, icu, libopus
   , libevent, expat, libjpeg, snappy
   , libpng, libxml2, libxslt, v8
  -, xdg_utils, yasm, zlib
  +, xdg_utils, yasm, zlib, libwebp
   , libusb1, libexif, pciutils
   
   , python, pythonPackages, perl, pkgconfig
  
positive.code:     use_system_harfbuzz = false;
      use_system_icu = false; # Doesn't support ICU 52 yet.
      use_system_libusb = false; # http://crbug.com/266149
      use_system_libwebp = false; # http://crbug.com/133161
      use_system_skia = false;
      use_system_sqlite = false; # http://crbug.com/22208
      use_system_v8 = !versionOlder src.version "34.0.0.0";
  
negative.code:     use_system_libexif = true;
      use_system_libjpeg = true;
      use_system_libpng = false; # PNG dlopen() version conflict
      use_system_libwebp = true;
      use_system_libxml = true;
      use_system_opus = true;
      use_system_snappy = true;
  