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