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This logic was simplified and made more robust with
http://crrev.com/848003006, but there is still a report that this is still a
problem.

I am suspicious of the popover detection logic. The popover could belong
to any window, and could be in the middle of fading in or out. Change the
logic to a hopefully more robust on-demand detection using
[NSApplication targetForAction:@selector(performClose:].

BUG=47134

Review URL: https://codereview.chromium.org/1025793002

Cr-Commit-Position: refs/heads/master@{#322075}