Check libpng directly into third_party/

third_party/libpng/tests/pngstest

+#!/bin/sh
+#
+# Usage:
+#
+#  tests/pngstest gamma alpha
+#
+# Run ./pngstest on the PNG files in $srcdir/contrib/testpngs which have the
+# given gamma and opacity:
+#
+#  gamma: one of; linear, 1.8, sRGB, none.
+#  alpha: one of; opaque, tRNS, alpha, none.  'none' is equivalent to !alpha
+#
+# NOTE: the temporary files pngstest generates have the base name gamma-alpha to
+# avoid issues with make -j
+#
+gamma="$1"
+shift
+alpha="$1"
+shift
+args=
+LC_ALL="C" # fix glob sort order to ASCII:
+for f in "${srcdir}/contrib/testpngs/"*.png
+do
+   g=
+   case "$f" in
+      *-linear[.-]*)
+         test "$gamma" = "linear" && g="$f";;
+
+      *-sRGB[.-]*)
+         test "$gamma" = "sRGB" && g="$f";;
+
+      *-1.8[.-]*)
+         test "$gamma" = "1.8" && g="$f";;
+
+      *)
+         test "$gamma" = "none" && g="$f";;
+   esac
+
+   case "$g" in
+      "")
+         :;;
+
+      *-alpha[-.]*)
+         test "$alpha" = "alpha" && args="$args $g";;
+
+      *-tRNS[-.]*)
+         test "$alpha" = "tRNS" -o "$alpha" = "none" && args="$args $g";;
+
+      *)
+         test "$alpha" = "opaque" -o "$alpha" = "none" && args="$args $g";;
+   esac
+done
+# This only works if the arguments don't contain spaces; they don't.
+exec ./pngstest --tmpfile "${gamma}-${alpha}-" --log ${1+"$@"} $args