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Previously, it was part of search.mojom, but this was confusing since
it's not fully related to search. Actual search functionality is added
in follow-up CL
https://chromium-review.googlesource.com/c/chromium/src/+/2103523/.

Bug: 1059099
Change-Id: I1bb14f678a56aef6025bb53485f9e72021557b1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2109236Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Auto-Submit: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751640}