anchor.diff:    }
   
     /// TODO(ahe): Clean this up.
  -  Token parseStuff(Token token, Function beginStuff, Function stuffParser,
  +  Token parseStuffOpt(Token token, Function beginStuff, Function stuffParser,
         Function endStuff, Function handleNoStuff) {
  -    // TODO(brianwilkerson): Rename to `parseStuffOpt`?
  -
       // TODO(brianwilkerson): Remove the invocation of `previous` when
       // `injectGenericCommentTypeList` returns the last consumed token.
       token = listener.injectGenericCommentTypeList(token.next).previous;
  
positive.code:   }
  
    Token parseTypeVariablesOpt(Token token) {
      return parseStuff(
          token,
          (t) => listener.beginTypeVariables(t),
          (t) => parseTypeVariable(t),
  
negative.code:   }
  
    Token parseTypeArgumentsOpt(Token token) {
      return parseStuffOpt(
          token,
          (t) => listener.beginTypeArguments(t),
          (t) => parseType(t),
  