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

samples/tests/dartc/test_config.dart

 // Copyright (c) 2011, 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("client_dartc_test_config");
 
+#import("dart:io");
 #import("../../../tools/testing/dart/test_suite.dart");
 
 class SamplesDartcTestSuite extends DartcCompilationTestSuite {
   SamplesDartcTestSuite(Map configuration)
       : super(configuration,
               'dartc',
               'samples',
               [ 'actors',
                 'belay',
                 'calculator',
@@ skipping 18 matching lines @@
                 'time',
                 'ui_lib',
               ],
               ['samples/tests/dartc/dartc.status']);
 
   bool isTestFile(String filename) {
     if (!filename.endsWith(".dart")) return false;
     // Using readOptionsFromFile here causes the file to be read twice,
     // because readOptionsFromFile is called again in the superclass.
     // Avoid this in new code.
-    return readOptionsFromFile(filename)["containsLeadingHash"];
+    return readOptionsFromFile(new Path.fromNative(filename))
+        ["containsLeadingHash"];
   }
 
   bool listRecursively() => true;
 }