[canvaskit] Fix whitespace constant definition.

Also some includes that I noticed along the way.

Change-Id: If48a3a9ff8bd5daea21065051c811e8b3e8a701f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/402136
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed