tools/testing: move code into individual libraries

tools/testing/dart/record_and_replay.dart

 // Copyright (c) 2012, 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.
 
 library record_and_replay;
 
 import 'dart:io';
 import 'dart:convert';
 
+import 'path.dart';
 import 'test_runner.dart';
-import 'utils.dart' show Path;
 
 /*
  * Json files look like this:
  *
  * [
  *   {
  *     'name' : '...',
  *     'command' : {
  *       'timeout_limit' : 60,
  *       'executable' : '...',
@@ skipping 105 matching lines @@
         duration,
         false);
     return commandOutput;
   }
 
   String _indexKey(String executable, String arguments) {
     return "${executable}__$arguments";
   }
 }