changeResponder = function(nextResponderInst, blockHostResponder) {
  var oldResponderInst = responderInst;
  responderInst = nextResponderInst;
  if (ResponderEventPlugin.GlobalResponderHandler !== null) {
    ResponderEventPlugin.GlobalResponderHandler.onChange(
      oldResponderInst,
      nextResponderInst,
      blockHostResponder
    );
  }
}
Last reported number of active touches.