add store_ffff, upgrade some tests

Yep, I forgot clamping in store_8888...

Change-Id: Ia129ec9b05b59d4018c8b633d44243bb37cf2c80
Reviewed-on: https://skia-review.googlesource.com/94360
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed