Merge "Revert of sdf: use linear edge distance approximation for all gradient directions (patchset #1 id:1 of https://codereview.chromium.org/1545893003/ )" into master-skia

https://skia.googlesource.com/skia/+/31d59e71cf5a571ff903d64ba2a6f17b715bfcfb

Change-Id: I5e9818bfb68db8d277861e5b41684d65bae59a8d