[canvaskit] Pass in paints via reference

I don't believe this impacts performance, but we'll see.

Change-Id: I5eb0843c186b61f4d34162c6fbc25c92b49a55a9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/315862
Reviewed-by: Nathaniel Nifong <nifong@google.com>
1 file changed