Fixes for saveBehind/drawBehind

- fixes bug in device restore (was passing the wrong matrix)
- use drawbehind for the clear, to avoid rounding differences between canvas and gpu

Change-Id: I9c130e38437d8d34242620750f11a6ae7e62ff97
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209801
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
(cherry picked from commit 9adc82c73df0ef25b708cae8aa48ef9c39ed4c67)
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/211642
Auto-Submit: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>