SkTypeface::onOpenStream to return unique_ptr.

This moves the smart pointer use up one more level in preparation for
changing SkTypeface::openStream to return unique_ptr as well.

Change-Id: Ib8173d59e03de38b06f6e1b4e6776f1961055ae7
Reviewed-on: https://skia-review.googlesource.com/c/195121
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
19 files changed