Mac: Possible fix for Cmd-W closing window instead of a tab
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}