Take const ref in is(Right|Left)Of

Start making things const ref that can never mutate. This
will help understanding of mutation flow in the code.

Change-Id: I0dd4b8c63eb0a2d018c5cf940eea88c553030540
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/690799
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
2 files changed