anchor.diff:  
   void indexSet(var a, var index, var value) {
     if (isJsArray(a)) {
  -    if (!(index is int)) {
  +    if (index is !int) {
         throw new IllegalArgumentException(index);
       }
       if (index < 0 || index >= a.length) {
  
positive.code: 
  tdiv(var a, var b) {
    if (checkNumbers(a, b)) {
      return (a / b).truncate();
    }
    return UNINTERCEPTED(a ~/ b);
  
negative.code: shr(var a, var b) {
    // TODO(floitsch): inputs must be integers.
    if (checkNumbers(a, b)) {
      // TODO(floitsch): Find cleaner way of forcing the type.
      a = JS('num', '#', a);
      b = JS('num', '#', b);
      if (b < 0) throw new IllegalArgumentException(b);
      // JavaScript only looks at the last 5 bits of the shift-amount. Shifting
      // by 33 is hence equivalent to a shift by 1.
  