SkPDF: add SK_API to new public factory.

Change-Id: I2396cb156d486f65d49a5f83a34886007b36026a
Reviewed-on: https://skia-review.googlesource.com/156009
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed