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There could be an ordering issue with the teardown
of a tab with an infobar after the infobar change
in r547527. Watch the "infobar manager gone" callback
and ensure a correct order.

For correctness, this makes the change in all the
other places that change used the infobar observer
except for InfoBarObserver, which is changed this
way in https://crrev.com/c/991468 .

BUG=354380, 828552

Change-Id: I21add007c5b2d725dc2985cbd268d3d4674978b6
Reviewed-on: https://chromium-review.googlesource.com/996372Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548246}