anchor.diff:      debugEvent("Part");
       StringLiteral uri = pop();
       List<Annotation> metadata = pop();
  -    Comment comment = null; // TODO(paulberry)
  +    // TODO(paulberry): capture doc comments.  See dartbug.com/28851.
  +    Comment comment = null;
       push(ast.partDirective(comment, metadata, toAnalyzerToken(partKeyword), uri,
           toAnalyzerToken(semicolon)));
     }
  
positive.code:     assert(modifiers == null); // TODO(paulberry)
      analyzer.Token abstractKeyword;
      List<Annotation> metadata = pop();
      Comment comment = null; // TODO(paulberry)
      push(ast.classTypeAlias(
          comment,
          metadata,
  
negative.code:     StringLiteral uri = pop();
      List<Annotation> metadata = pop();
      assert(metadata == null);
      // TODO(paulberry): capture doc comments.  See dartbug.com/28851.
      Comment comment = null;
      push(ast.importDirective(
          comment,
  