SkPDF:  minor cleanups of skpdfdevice

Change-Id: I2143daaa6061003d8631f38ea39724fb12d494db
Reviewed-on: https://skia-review.googlesource.com/24747
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
2 files changed