add behavior enum to SkTypeface::serialize()

This enables a simple SkSerialProc for typefaces that can decide,
during picture serialization, how much data to serialize for each
typeface.

Bug: skia:
Change-Id: Ic9d18b24d9e650fd2a78304520a73aa0645dc139
Reviewed-on: https://skia-review.googlesource.com/150968
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Yuqian Li <liyuqian@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
5 files changed