Event.cancelBubble cannot be used for stopping event propagation in Polymer

[dfreedm]

In IE 10, event.cancelBubble is readonly. This breaks the event coalescing mechanism in Polymer for the on-event syntax.

Here's a simple test case

var e = document.createEvent('Event');
e.initEvent('foo', true, true);
var cb = e.cancelBubble;
e.cancelBubble = !e.cancelBubble;
if (cb !== e.cancelBubble) {
  console.log('writable');
} else {
  console.log('readonly');
}

On Firefox, Safari, and Chrome: writable.
On IE: readonly.

Related to #259

[sjmiles]

Believe this question has died of old age.