DO NOT MERGE Update libpng to 1.6.20

BUG:23265085
Change-Id: I85199805636d771f3597b691b63bc0bf46084833
(cherry picked from commit bbe98b40cda082024b669fa508931042eed18f82)
diff --git a/tests/pngimage-quick b/tests/pngimage-quick
index 2d4b5db..328dc27 100755
--- a/tests/pngimage-quick
+++ b/tests/pngimage-quick
@@ -1,2 +1,2 @@
 #!/bin/sh
-exec ./pngimage --log "${srcdir}/contrib/pngsuite/"*.png
+exec ./pngimage --list-combos --log "${srcdir}/contrib/pngsuite/"*.png