minor cleanups in newly privatized device headers

BUG=skia:

Change-Id: Id6ebd54f404b5f0869d96368b98957ac10a2083f
NOTREECHECKS=True
Reviewed-on: https://skia-review.googlesource.com/7369
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
2 files changed