add device-clipping to gpudevice

BUG=skia:

Change-Id: Id8c8994d4bddf591e1205ed9d591f4fce7d3af99
Reviewed-on: https://skia-review.googlesource.com/8531
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
7 files changed