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Previously the code was imperatively registering such listeners on
|document.body| which was unnecessary. Moreover, adding meaningful
type checking for such listeners, since previously they were lacking
type info.

Bug: None
Change-Id: I1041f0becf89d1f88b03a1ad2dc9ec9e85a99e4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2304956
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Auto-Submit: dpapad <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789722}