GitLab

Add data structures for tracking glyph usage. There are two variants
sparse and dense and which one is used should depend on the font being
subset, this can be done heuristically before starting tracking to
minimize memory overhead.

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

Bug: 1006242
Change-Id: I251fae2270386ea0279268db4ffef8e98942e278
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1816440Reviewed-by: Ian Vollick <vollick@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699716}