disable coverage optimization for hairlines

The coverage blitter is an optimization of regular blitting to A8.
It can go faster because it never tries to blend with itself... because
it was intended to be called only by fill-path, which is written to
never draw twice in the same place. Hairlines don't make this promise,
so we can use the coverage optimization for hairlines.

Change-Id: I0a4816f886462017ad81378d5928357ef038ae8f
Reviewed-on: https://skia-review.googlesource.com/18666
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed