function SyntheticEvent(dispatchConfig, dispatchMarker, nativeEvent) {
  this.dispatchConfig = dispatchConfig;
  this.dispatchMarker = dispatchMarker;
  this.nativeEvent = nativeEvent;

  var Interface = this.constructor.Interface;
  for (var propName in Interface) {
    if (!Interface.hasOwnProperty(propName)) {
      continue;
    }
    var normalize = Interface[propName];
    if (normalize) {
      this[propName] = normalize(nativeEvent);
    } else {
      this[propName] = nativeEvent[propName];
    }
  }

  var defaultPrevented = nativeEvent.defaultPrevented != null ?
    nativeEvent.defaultPrevented :
    nativeEvent.returnValue === false;
  if (defaultPrevented) {
    this.isDefaultPrevented = emptyFunction.thatReturnsTrue;
  } else {
    this.isDefaultPrevented = emptyFunction.thatReturnsFalse;
  }
  this.isPropagationStopped = emptyFunction.thatReturnsFalse;
}
Helper to reduce boilerplate when creating subclasses.

@param {function} Class
@param {?object} Interface