This fixes following cases which causes hotkey action accidentally:
* hitting Esc key to cancel text composition (mostly in CJK)
Although events on cancelling composition are still heavily
browser / input method dependent, but this implementation would
covers current UI Events spec and some exceptions.
* hitting Esc key to close autocomplete suggestions
This PR changes to use keydown event instead of keyup event as well as other hotkeys.
4e35ce8269