anchor.diff:            }
           }
         } else if (name == 'codeUnitAt') {
  -        if (node.arguments.length == 2) {
  +        if (node.dartArgumentsLength == 1) {
             Primitive index = node.dartArgument(0);
             if (lattice.isDefinitelyString(receiverValue) &&
                 lattice.isDefinitelyInt(getValue(index))) {
  
positive.code:       UnaryOperator operator = UnaryOperator.parse(opname);
        AbstractConstantValue result = lattice.unaryOp(operator, receiver);
        return finish(result, canReplace: !receiver.isNullable);
      } else if (node.arguments.length == 2) {
        // Binary operator.
        AbstractConstantValue right = getValue(node.dartArgument(0));
        BinaryOperator operator = BinaryOperator.parse(opname);
  
negative.code: 
      // Calculate the resulting constant if possible.
      String opname = node.selector.name;
      if (node.dartArgumentsLength == 0) {
        // Unary operator.
        if (opname == "unary-") {
          opname = "-";
  