Allow providing SkExecutor to SkThreadedBMPDevice

So that callers could manage the thread pool themselves instead of
relying on SkThreadBMPDevice.

Bug: skia:
Change-Id: Idbeafc9ac5d111370fd1b74f6eab9ac8df179940
Reviewed-on: https://skia-review.googlesource.com/39760
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>
2 files changed