Build the Android version of PNG on Android.

Fixes Android build failures.

Android builds a custom version of libpng (instead of the one
determined by skia_libpng_static) which supplies extra needed
functions.

TBR=mtklein@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/971243003
1 file changed