Add test that SWPathRenderer GenIDChange listeners get removed.

When a cached path mask texture is destroyed it should remove the
gen ID change listener on from the SkPathRef:
https://skia-review.googlesource.com/c/skia/+/272654

Change-Id: I4d1781e578b29b801b1b5b97ba5119ac321de73c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/273004
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
5 files changed