Make GrRRectBlurEffect use the thread-safe uniquely-keyed view cache (take 2)

This yields a ~8% performance improvement on OOP-R/DDL-like rendering of the simpleblurroundrect GM.

Bug: 1108408
Change-Id: I710c75b73a395b2280abf0c5af528e0f6731326d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/311720
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/320917
5 files changed