GitLab

Moves the logic to demote autocomplete matches with headers to ACResult
where it is called after matches are deduped and sorted and before they
are culled. This step needs to happen before matches are culled so that
matches with higher relevance (remote ZPS) can be used to backfill
matches with lower relevance (local ZPS) before the lower relevance
ones are thrown away. The latter is a requirement for the Trending
suggestions experiment.

Also addresses a technical debt by grouping the matches with headers
in addition to demoting them to avoid interleaving of groups.

Bug: 1122669
Change-Id: Iba9fb9d02bc7ddd07805cfd31e32a84604da077c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2386839
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803591}