Change test scripts to use Path library in most places, instead of strings.

tools/test.dart

 #!/usr/bin/env 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.
 
 /**
  * This file is the entrypoint of the dart test suite.  This suite is used
  * to test:
  *
  *     1. the dart vm
  *     2. the frog compiler (compiles dart to js)
  *     3. the leg compiler (also compiles dart to js)
  *     4. the dartc static analyzer
  *     5. the dart core library
  *     6. other standard dart libraries (DOM bindings, ui libraries,
  *            io libraries etc.)
  *
  * This script is normally invoked by test.py.  (test.py finds the dart vm
  * and passses along all command line arguments to this script.)
  *
  * The command line args of this script are documented in
  * "tools/testing/test_options.dart".
  *
  */
 
 #library("test");
 
+#import("dart:io");
 #import("testing/dart/test_runner.dart");
 #import("testing/dart/test_options.dart");
 #import("testing/dart/test_suite.dart");
 
 #import("../compiler/tests/dartc/test_config.dart");
 #import("../runtime/tests/vm/test_config.dart");
 #import("../samples/tests/dartc/test_config.dart");
 #import("../tests/co19/test_config.dart");
 
 /**
@@ skipping 70 matching lines @@
         // vm tests contain both cc tests (added here) and dart tests (added in
         // [TEST_SUITE_DIRECTORIES]).
         queue.addTestSuite(new VMTestSuite(conf));
       } else if (conf['compiler'] == 'dartc' && key == 'dartc') {
         queue.addTestSuite(new SamplesDartcTestSuite(conf));
         queue.addTestSuite(new JUnitDartcTestSuite(conf));
       }
     }
 
     for (final testSuiteDir in TEST_SUITE_DIRECTORIES) {
-      final name = testSuiteDir.substring(testSuiteDir.lastIndexOf('/') + 1);
+      Path testSuitePath = new Path(testSuiteDir);
+      final name = testSuitePath.filename;
       if (selectors.containsKey(name)) {
         queue.addTestSuite(
-            new StandardTestSuite.forDirectory(conf, testSuiteDir));
+            new StandardTestSuite.forDirectory(conf, testSuitePath));
       }
     }
 
     return true;
   }
 
   // Start process queue.
   var queue = new ProcessQueue(maxProcesses,
                                progressIndicator,
                                startTime,
                                printTiming,
                                enqueueConfiguration,
                                verbose,
                                listTests);
 }