skip comments in benchmark code

pkg/analyzer_cli/tool/perf.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// An entrypoint used to run portions of analyzer and measure its performance.
 library analyzer_cli.tool.perf;
 
 import 'dart:async';
 import 'dart:io' show exit;
 
@@ skipping 169 matching lines @@
 }
 
 /// Scan [source] and return the first token produced by the scanner.
 Token tokenize(Source source) {
   scanTimer.start();
   var contents = source.contents.data;
   scanTotalChars += contents.length;
   // TODO(sigmund): is there a way to scan from a random-access-file without
   // first converting to String?
   var scanner = new Scanner(source, new CharSequenceReader(contents),
-      AnalysisErrorListener.NULL_LISTENER);
+      AnalysisErrorListener.NULL_LISTENER)..preserveComments = false;
   var token = scanner.tokenize();
   scanTimer.stop();
   return token;
 }
 
 /// Report that metric [name] took [time] micro-seconds to process
 /// [scanTotalChars] characters.
 void report(String name, int time) {
   var sb = new StringBuffer();
   sb.write('$name: $time us, ${time ~/ 1000} ms');
   sb.write(', ${scanTotalChars * 1000 ~/ time} chars/ms');
   print('$sb');
 }