Extract a PatchWriter::Patch base class

Bug: skia:12524
Change-Id: I48bd7dabb7d169f3ac544f2b7a2e2a68f4b01e1b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/474158
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
1 file changed