Confirm-to-quit: Close bubble when browser loses focus

Sometimes, another app can grab the focus while the confirm-to-quit bubble is
showing. When this happens, Chrome won't get the key release event and the
bubble will stay open forever.  The only way to close it would be to press
Ctrl+Shift+Q again, but this would close Chrome.

This CL closes the confirm-to-quit bubble and resets the state of the controller
when this happens.

BUG=243164
R=sky

Change-Id: I1800501be3cd4896876347ce2fb511a08e90eba7
Reviewed-on: https://chromium-review.googlesource.com/1069487
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561377}
3 files changed