GitLab

This CL adds basic subsetting support for paint previews. This depends
on Harfbuzz's subsetter and is based on the implementation in
SkPDFSubsetFont.

Part of landing:
https://chromium-review.googlesource.com/c/chromium/src/+/1786583

Bug: 1006242
Change-Id: I757543ab9a575dc829a6f2b7fc1bb9b89fef5c97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1816730Reviewed-by: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700264}