Refactor particle age logic

Move to a model that only needs floats, and puts the age in the
SkParticleState struct. Add a better test case for spawn affector
animation, to verify that things are still working.

Bug: skia:
Change-Id: I97d99de5f5d4cb302b76116e67ecc93368fb1677
Reviewed-on: https://skia-review.googlesource.com/c/193580
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed