EventDispatcher: Add comment about defensive copy in dispatchEvent.
@@ -68,6 +68,7 @@ Object.assign( EventDispatcher.prototype, {
event.target = this;
+ // Make a copy, in case listeners are removed while iterating.
var array = listenerArray.slice( 0 );
for ( var i = 0, l = array.length; i < l; i ++ ) {