move canReuse to sub runs

Part of the canReuse calculation is now handled by the SubRuns. This
allows a more precise calculation about the circumstances of reuse.

The change also spotlights, that the original whole blob canReuse
function my not have been very efficient. These inefficiencies are
maintained for now.

Change-Id: I7f8e725f578222e5c033d6ff8aa59dd3c5115e38
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/315319
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
2 files changed