[M56] More fixes for distance field paths

Disables use of SDFs for very small paths (because of blurring) and
adds a border of 1 pixel in device space to handle antialiasing.

BUG=chromium:677889

Change-Id: Icd2f7e80323b1255f8de52b97360e9a2d995c765
Reviewed-on: https://skia-review.googlesource.com/6895
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
3 files changed