Simplify canReuse calculation for TransformedMaskSubRun

The canReuse() calculation relied on an expensive calculation
on a constant matrix. Just store the needed result.

Bug: skia:14150
Change-Id: Ibcf01da703f81fcd4586191fe09532e209a79585
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/651438
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
1 file changed