use initial device coordinates as subrun positions

Originally, the positions had a bias of -initialOrigin,
so all that was needed was to add the new drawingOrigin
in. Store the actual device coordinates thus eliminating
the -initialOrigin, and calculate the origin offset
drawingOrigin - initialOrigin at vertex fill time.

Change-Id: I5a7fe0074f0c7fd01c5fe90a47e67509631379fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/333127
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
3 files changed