Add init-once to threaded backend

For the simplicity of this CL, I haven't enabled DAA for init-once yet.
The current init-once is only enabled for draw path, and it simply
generates the dev path in the init-once phase.

Bug: skia:
Change-Id: Ie9a9ef9fc453acbdeb48b06b93d578c626961e3f
Reviewed-on: https://skia-review.googlesource.com/87784
Commit-Queue: Yuqian Li <liyuqian@google.com>
Reviewed-by: Herb Derby <herb@google.com>
11 files changed