Note typeface usage in layers.

Typeface usage in layers was not propagated back up to the top level,
so it is easy to lose track of typefaces when layers are used.

Change-Id: I464325c0d9bce7c41592e78855ee0e21e2e6e5be
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290816
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
2 files changed