Encapsulate the SDF loop

Change-Id: Ib7c6bcc0ccb39224c1d6be3df4f342bd7e58d69e
Reviewed-on: https://skia-review.googlesource.com/148220
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed