Break up InitDistanceFieldPaint Break InitDistanceFieldPaint along code that is common and, code that is specific to GPU. Change-Id: Ic831491829fe402a46f4e612c2598d987ae19c8c Reviewed-on: https://skia-review.googlesource.com/c/193371 Reviewed-by: Mike Klein <mtklein@google.com> Commit-Queue: Herb Derby <herb@google.com>