Use ARM fixes for SDF encoding.

This pulls out the encoding fixes by Joel Liang from
https://codereview.chromium.org/1643143002/
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1726763002

Review URL: https://codereview.chromium.org/1726763002
2 files changed