Add .fromPath constructors to File and Directory.

tests/standalone/io/directory_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.
 //
 // Directory listing test.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class DirectoryTest {
@@ skipping 302 matching lines @@
     });
   }
 
   static void testCurrent() {
     Directory current = new Directory.current();
     if (Platform.operatingSystem != "windows") {
       Expect.equals("/", current.path.substring(0, 1));
     }
   }
 
+  static void testFromPath() {
+    var name = new File('.').fullPathSync();
+    Directory current1 = new Directory(name);
+    var path = new Path.fromNative(name);
+    Directory current2 = new Directory.fromPath(path);
+    Expect.equals(current1.path, current2.path);
+    Expect.isTrue(current1.existsSync());
+  }
+
   static void testMain() {
     testListing();
     testListNonExistent();
     testListTooLongName();
     testDeleteNonExistent();
     testDeleteTooLongName();
     testDeleteNonExistentSync();
     testDeleteTooLongNameSync();
     testExistsCreateDelete();
     testExistsCreateDeleteSync();
     testCreateTemp();
     testCreateDeleteTemp();
     testCurrent();
+    testFromPath();
   }
 }
 
 
 class NestedTempDirectoryTest {
   List<Directory> createdDirectories;
   Directory current;
 
   NestedTempDirectoryTest.run()
       : createdDirectories = new List<Directory>() {
@@ skipping 81 matching lines @@
 }
 
 
 main() {
   DirectoryTest.testMain();
   NestedTempDirectoryTest.testMain();
   testCreateTempErrorSync();
   testCreateTempError();
   testRename();
 }