Restore custom dismissal method for extension popups.

Using the default method as in
https://chromium-review.googlesource.com/c/chromium/src/+/1367129 prevents
extension popups from opening their own popup windows, e.g. JS alerts.  Since
there's no plan to deprecate that functionality and we can't come up with a good
alternate route, this restores part of the previous code.

This does not re-introduce the problem with long clicks re-showing the popup;
that was sufficiently addressed by the rest of the previous CL.

Bug: 941994
Change-Id: I59bb7d695b51e250a096b8ca8331876593507ead
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529753
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642391}
2 files changed