Gestures.handleNative sometimes throws "Unable to get property mousedown of undefined or null reference" in IE11

[wicksell]

When using <paper-dropdown-menu> and selecting an item in IE11 I get the error "Unable to get property mousedown of undefined or null reference". The error originates from Gestures.handleNative. The statement node[GESTURE_KEY] is undefined. If i add the following line

    if (!gobj) gobj = unwrap(node)[GESTURE_KEY];

everything works perfect. So the problem seems to be that the node is not wrapped when passed to Gestures.add but is when the event is received.

[wicksell]

I have investigated my problem further and found that it may be related to #1001. A change to iron-overlay-behavior adds a gesture listener on document, see PolymerElements/iron-overlay-behavior@ad1cda0. On registration document is not wrapped but webcomponentsjs always wrap events when Shadow DOM is polyfilled so in Gestures.handleNative the event target is wrapped and thus the property GESTURE_KEY is not available.

[dfreedm]

Just need to land webcomponents/webcomponentsjs#434 first, then I can make this work as expected.