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- Do not reroute events if it is targetted to the tray or its
  descendants, or if target of the event has window of the tray as a
  transient ancestor.
- When network info bubble is shown, the bubble is active but the tray
  itself is not active. The bubble is shown as another widget. The
  bubble should receive key events in this case. If the handler reroutes
  key events in this case, the tray is closed when esc key is pressed
  while the bubble is shown.

      information icon. Press esc key to close the info bubble. Confirm
      that it only closes the info bubble.

Bug: 758530
Test: Open network section of system tray by click. Click the
Change-Id: I0df0c81e4df28785f16fdefb9af37a73f00ef604
Reviewed-on: https://chromium-review.googlesource.com/776255Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Yuki Awano <yawano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523384}