Make glyph runs const in the glyph run list.

Change-Id: I5627eef258abc506675b389a9d72692f92fd823e
Reviewed-on: https://skia-review.googlesource.com/c/167922
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
3 files changed