[skottie] External font loader tweaks

More general ResourceProvider font loading API:

1) font name argument
2) invoked unconditionally (regardless of whether an URL is present)

This provides more font control to the embedder.

Change-Id: I95557c75c2e0fe41ff68ee1b6cec8929405a74fc
Reviewed-on: https://skia-review.googlesource.com/157424
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
4 files changed