Use '&' to toggle showing the gm's size in viewer

Bug: skia:
Change-Id: Id294b6a48d60d95b46ce3443edf10513599c43d1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201230
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
3 files changed