anchor.diff:    }
   
     Token parseNativeClause(Token nativeToken) {
  +    assert(optional('native', nativeToken));
       Token token = nativeToken.next;
       bool hasName = false;
       if (token.kind == STRING_TOKEN) {
  
positive.code:       listener.handleNativeFunctionBodyIgnored(nativeToken, token);
        // Fall through to recover and skip function body
      }
      token = token;
      String value = token.stringValue;
      if (identical(value, ';')) {
        if (!allowAbstract) {
  
negative.code:   /// ```
    Token parseOptionalFormalParameters(
        Token token, bool isNamed, MemberKind kind) {
      assert(isNamed ? optional('{', token) : optional('[', token));
      Token begin = token;
      listener.beginOptionalFormalParameters(begin);
      int parameterCount = 0;
  