Revert "Remove SkPDFDocument and SkPDFDevice from the public headers."

This reverts commit 8b1f761365df6652ea9304b6572d2dd91917b9aa.

BUG=skia:
TBR=
NOTRY=True
NOTREECHECKS=True

Review URL: https://codereview.chromium.org/839603002
6 files changed