Partially defer GrSWMaskHelper

This is intended to position the writePixels in GrSWMaskHelper::toTexture for moving to GrSurfaceContext

Change-Id: I6c3d24eb3b1db3b0efc63f7f4f1240a7a00ee88a
Reviewed-on: https://skia-review.googlesource.com/6032
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
12 files changed