anchor.diff:  
     @override
     void set returnType(TypeAnnotation type) {
  -    _returnType = _becomeParentOf(type as AstNodeImpl);
  +    _returnType = _becomeParentOf(type as TypeAnnotationImpl);
     }
   
     @override
  
positive.code:    * The message to report if the assertion fails, or `null` if no message was
     * supplied.
     */
    Expression _message;
  
    @override
    Token rightParenthesis;
  
negative.code:    * The statement that is executed if the condition evaluates to `false`, or
     * `null` if there is no else statement.
     */
    StatementImpl _elseStatement;
  
    /**
     * Initialize a newly created if statement. The [elseKeyword] and
  