add virtual to support CTFontRef

Bug: skia:6583
Change-Id: I8525e63d3f43467289360d4b15c0153d2a43539e
Reviewed-on: https://skia-review.googlesource.com/15194
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed