More png API compatibility

BUG=skia:

Change-Id: I71aa730b08b3eebd18d9651363bbcd816b8598fd
Reviewed-on: https://skia-review.googlesource.com/9976
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed