Move hasW to SubRun

Ecapsulate SubRunType better by moving hasW
to subRun.

* Split out implementation of firstSubRun()

Change-Id: Ibb037d495a921c99f318596992187b1b3c1e0725
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292842
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed