Cache runtime color filter alpha-unchanged flag on the effect

This reuses the work we're already doing to compute the one-at-a-time
program, and lets us share the result across color filter instances
created from the same effect.

When we added caching of the flag to filter creation, pinpoint found a
performance regression. I expect this to resolve that.

Bug: chromium:1187432
Change-Id: Ie4f8551fa432d298ce950cba8642b9de28f19b81
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/396758
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed