[canvaskit] Add support for external fonts

We ignore the url for web fonts, as we assume the names
will not collide.

Bug: skia:
Change-Id: Ifaaa0d27e0de2c5088bc0885c9299bb83ee78a5d
Reviewed-on: https://skia-review.googlesource.com/c/196426
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
6 files changed