Fix path tests on windows.

utils/tests/pub/path/path_windows_test.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 path_test;
 
 import 'dart:io' as io;
 
 import '../../../../pkg/unittest/lib/unittest.dart';
 import '../../../pub/path.dart' as path;
@@ skipping 208 matching lines @@
     });
 
     group('from relative root', () {
       var r = new path.Builder(style: path.Style.windows, root: r'foo\bar');
 
       // These tests rely on the current working directory, so don't do the
       // right thing if you run them on the wrong platform.
       if (io.Platform.operatingSystem == 'windows') {
         test('given absolute path', () {
           var b = new path.Builder(style: path.Style.windows);
-          expect(r.relative(r'C:\'), b.join(b.relative(r'C:\'), r'..\..'));
-          expect(r.relative(r'C:\a\b'),
-              b.join(b.relative(r'C:\'), r'..\..\a\b'));
+          // TODO(rnystrom): Use a path method here to get the root prefix
+          // when one exists.
+          var drive = path.current.substring(0, 3);
+          expect(r.relative(drive), b.join(b.relative(drive), r'..\..'));
+          expect(r.relative(b.join(drive, r'a\b')),
+              b.join(b.relative(drive), r'..\..\a\b'));
+
+          // TODO(rnystrom): Test behavior when drive letters differ.
         });
       }
 
       test('given relative path', () {
         // The path is considered relative to the root, so it basically just
         // normalizes.
         expect(r.relative(''), '.');
         expect(r.relative('.'), '.');
         expect(r.relative('..'), '..');
         expect(r.relative('a'), 'a');
@@ skipping 44 matching lines @@
     expect(builder.withoutExtension(r'a\b.c.d'), r'a\b.c');
     expect(builder.withoutExtension(r'a\'), r'a\');
     expect(builder.withoutExtension(r'a\b\'), r'a\b\');
     expect(builder.withoutExtension(r'a\.'), r'a\.');
     expect(builder.withoutExtension(r'a\.b'), r'a\.b');
     expect(builder.withoutExtension(r'a.b\c'), r'a.b\c');
     expect(builder.withoutExtension(r'a\b/c'), r'a\b/c');
     expect(builder.withoutExtension(r'a\b/c.d'), r'a\b/c');
   });
 }