DM: use SkPngEncoder

Change-Id: If1360bee50c8c360e4b1edf09c8a39aa32a59eb9
Reviewed-on: https://skia-review.googlesource.com/19520
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed