Remove unnecessary indexing passes from serialization.

test/serialize_bench.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.
+import 'package:kernel/kernel.dart';
+import 'dart:io';
+
+final String usage = '''
+Usage: serialize_bench INPUT.dill OUTPUT.dill
+
+Deserialize INPUT and write it back to OUTPUT several times, measuring
+the time it takes, including I/O time.
+''';
+
+main(List<String> args) async {
+  if (args.length != 2) {
+    print(usage);
+    exit(1);
+  }
+  Program program = loadProgramFromBinary(args[0]);
+
+  String destination = args[1];
+  var watch = new Stopwatch()..start();
+  await writeProgramToBinary(program, destination);
+  int coldTime = watch.elapsedMilliseconds;
+
+  watch.reset();
+  int numTrials = 10;
+  for (int i = 0; i < numTrials; ++i) {
+    await writeProgramToBinary(program, destination);
+  }
+  double hotTime = watch.elapsedMilliseconds / numTrials;
+
+  print('Cold time: $coldTime ms');
+  print('Hot time:  $hotTime ms');
+}