use common intermediate device class for clipstack management

BUG=skia:6214

Change-Id: I64b849ad7c8dafe423e24e6fccfb3f0c1d096ab0
Reviewed-on: https://skia-review.googlesource.com/8669
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
9 files changed