Add use counters for :host-context() in both profiles.

Adding use counters for both snapshot and live in case we can remove
from one profile and not the other.

This was discussed at a CSSWG F2F. See [1].

[1] https://github.com/w3c/csswg-drafts/issues/1914

Bug: 936225
Change-Id: Ide3cd3991026a350711beca225da4a49a532e952
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1508456
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639469}
4 files changed