anchor.diff:    /// report an error if [element] does not typecheck.
     ConstantExpression internalCompileVariable(
         VariableElement element, bool isConst, bool checkType) {
  -    if (_initialVariableValues.containsKey(element.declaration)) {
  -      ConstantExpression result = _initialVariableValues[element.declaration];
  +    if (initialVariableValues.containsKey(element.declaration)) {
  +      ConstantExpression result = initialVariableValues[element.declaration];
         return result;
       }
       if (element.hasConstant) {
  
positive.code:   @override
    @deprecated
    ConstantValue getConstantValueForVariable(VariableElement element) {
      return getConstantValue(_initialVariableValues[element.declaration]);
    }
  
    ConstantExpression compileConstant(VariableElement element) {
  
negative.code:     }
      if (expression != null) {
        element.constant = expression;
        initialVariableValues[element.declaration] = expression;
      } else {
        assert(invariant(element, !isConst,
            message: "Variable $element does not compile to a constant."));
  