The patched event object contains the following members:
 - type           {String}    Event type, e.g. 'click'
 - timestamp      {Date}      A date object for when the event was fired
 - target         {Object}    The element that actually triggered the event
 - currentTarget  {Object}    The element the listener is attached to
 - relatedTarget  {Object}    For mouseover and mouseout, the previous object
 - offsetX        {Number}    X-coordinate relative to target
 - offsetY        {Number}    Y-coordinate relative to target
 - clientX        {Number}    X-coordinate relative to viewport
 - clientY        {Number}    Y-coordinate relative to viewport
 - screenX        {Number}    X-coordinate relative to the edge of the screen
 - screenY        {Number}    Y-coordinate relative to the edge of the screen
 - button         {Number}    Mouse button. Use isButton() to test.
 - keyCode        {Number}    Key-code
 - ctrlKey        {Boolean}   Was ctrl key depressed
 - altKey         {Boolean}   Was alt key depressed
 - shiftKey       {Boolean}   Was shift key depressed
 - metaKey        {Boolean}   Was meta key depressed

 NOTE: The keyCode member contains the raw browser keyCode. For normalized
 key and character code use {@link goog.events.KeyHandler}.