This CL makes it explicit that the unit tests always get a direct context.
It is mainly a mechanical CL.
Change-Id: I49e0628851d9c81eb47386ef978edf905c6469d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299866
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>