Optimize pushing duplicates of 0.

Rather than writing a zero and then swizzling out duplicates, we can
just zero out a range of slots directly. This happens often enough
that it's worth optimizing.

Change-Id: Ic5d9bf1b37d0c61f72056ccd0025e850938393fd
Bug: skia:13676
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/632696
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
21 files changed