anchor.diff:  #source('native_helper.dart');
   #source('regexp_helper.dart');
   #source('string_helper.dart');
  +
  +// Performance critical helper methods.
  +add(var a, var b) => (a is num && b is num)
  +    ? JS('num', @'# + #', a, b)
  +    : add$slow(a, b);
  +
  +sub(var a, var b) => (a is num && b is num)
  +    ? JS('num', @'# - #', a, b)
  +    : sub$slow(a, b);
  +
  +div(var a, var b) => (a is num && b is num)
  +    ? JS('num', @'# / #', a, b)
  +    : div$slow(a, b);
  +
  +mul(var a, var b) => (a is num && b is num)
  +    ? JS('num', @'# * #', a, b)
  +    : mul$slow(a, b);
  +
  +index(var a, var index) {
  +  // The type test may cause a NullPointerException to be thrown but
  +  // that matches the specification of what the indexing operator is
  +  // supposed to do.
  +  bool isJsArrayOrString = JS('bool',
  +      @'typeof # == "string" || #.constructor === Array',
  +      a, a);
  +  if (isJsArrayOrString) {
  +    var key = JS('int', '# >>> 0', index);
  +    if (key === index && key < JS('int', @'#.length', a)) {
  +      return JS('var', @'#[#]', a, key);
  +    }
  +  }
  +  return index$slow(a, index);
  +}
  +
  +indexSet(var a, var index, var value) {
  +  // The type test may cause a NullPointerException to be thrown but
  +  // that matches the specification of what the indexing operator is
  +  // supposed to do.
  +  bool isMutableJsArray = JS('bool',
  +      @'#.constructor === Array && !#.immutable$list',
  +      a, a);
  +  if (isMutableJsArray) {
  +    var key = JS('int', '# >>> 0', index);
  +    if (key === index && key < JS('int', @'#.length', a)) {
  +      JS('void', @'#[#] = #', a, key, value);
  +      return;
  +    }
  +  }
  +  indexSet$slow(a, index, value);
  +}
   
   /**
    * Returns true if both arguments are numbers.
  
positive.code:   return UNINTERCEPTED(a[index]);
  }
  
  void indexSet(var a, var index, var value) {
    if (isJsArray(a)) {
      if (index is !int) {
        throw new IllegalArgumentException(index);
  
negative.code:   return value !== null && JS('bool', @'#.constructor === Array', value);
  }
  
  add$slow(var a, var b) {
    if (checkNumbers(a, b)) {
      return JS('num', @'# + #', a, b);
    } else if (a is String) {
  