Always render GPU masks with AA rendering

This makes Ganesh match the raster backend's behavior.

It, unfortunately, will alter the following GMs:

blurrects
blur2rects
bleed_alpha_*
bleed_*

Change-Id: Id8cfbe8776e8e8a11fce9d09863b4244a72fb1ce
Reviewed-on: https://skia-review.googlesource.com/148994
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
3 files changed