Silence unused-variable warning for layerHeight.

`layerHeight` is only used in an assert, so in release builds, it's not
actually used for anything.

Change-Id: I6fd802dd4a4f29bd01c469b80697366d4f4bb7d6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/445966
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
1 file changed