Remove the Path class from dart:io

tests/lib/mirrors/library_uri_io_test.dart

 // Copyright (c) 2013, 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.
 
 // Test library uri for a library read as a file.
 
 library MirrorsTest;
 
 import 'dart:mirrors';
 import 'dart:io';
 import '../../../pkg/unittest/lib/unittest.dart';
 
 class Class {
 }
 
 testLibraryUri(var value, Uri expectedUri) {
   var valueMirror = reflect(value);
   ClassMirror valueClass = valueMirror.type;
   LibraryMirror valueLibrary = valueClass.owner;
   expect(valueLibrary.uri, equals(expectedUri));
 }
 
 main() {
   var mirrors = currentMirrorSystem();
   test("Test current library uri", () {
     String appendSlash(String path) => path.endsWith('/') ? path : '$path/';
     Uri cwd = new Uri(
         scheme: 'file',
-        path: appendSlash(new Path(new File('.').fullPathSync()).toString()));
-    Uri uri = cwd.resolve(new Path(Platform.script).toString());
+        path: appendSlash(new File('.').fullPathSync()));
+    Uri uri = cwd.resolve(Platform.script);
     testLibraryUri(new Class(), uri);
   });
 }