anchor.diff:      return token;
     }
   
  +  /// ```
  +  /// statement:
  +  ///   label* nonLabelledStatement
  +  /// ;
  +  /// ```
     Token parseLabeledStatement(Token token) {
  +    // TODO(brianwilkerson): Enable this assert.
  +    // `parseType` is allowing `void` to be a label.
  +//    assert(token.isIdentifier);
  +    assert(optional(':', token.next));
       int labelCount = 0;
       do {
         token = parseLabel(token);
  
positive.code:     return token;
    }
  
    Token parseTopLevelDeclarationImpl(
        Token token, DirectiveContext directiveState) {
      if (identical(token.type, TokenType.SCRIPT_TAG)) {
  
negative.code:     return token;
    }
  
    /// ```
    /// expressionStatement:
    ///   expression? ';'
    /// ;
    /// ```
    Token parseExpressionStatement(Token token) {
      // TODO(brianwilkerson): If the next token is not the start of a valid
      // expression, then this method shouldn't report that we have an expression
      // statement.
      listener.beginExpressionStatement(token);
  