Add .fromPath constructors to File and Directory.

tests/standalone/io/file_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.
 //
 // Dart test program for testing file I/O.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class MyListOfOneElement implements List {
@@ skipping 959 matching lines @@
   static void testOpenDirectoryAsFileSync() {
     var f = new File('.');
     try {
       f.openSync();
       Expect.fail("Expected exception opening directory as file");
     } catch (var e) {
       Expect.isTrue(e is FileIOException);
     }
   }
 
+  static void testOpenFileFromPath() {
+    var name = getFilename("tests/vm/data/fixed_length_file");
+    var path = new Path(name);
+    var f = new File.fromPath(path);
+    Expect.isTrue(f.existsSync());
+    name = f.fullPathSync();
+    path = new Path.fromNative(name);
+    var g = new File.fromPath(path);
+    Expect.isTrue(g.existsSync());
+    Expect.equals(name, g.fullPathSync());
+  }
+
   static void testReadAsBytes() {
     var port = new ReceivePort();
     port.receive((result, replyTo) {
       port.close();
       Expect.equals(42, result);
     });
     var name = getFilename("tests/vm/data/fixed_length_file");
     var f = new File(name);
     f.readAsBytes().then((bytes) {
       Expect.isTrue(new String.fromCharCodes(bytes).endsWith("42 bytes."));
@@ skipping 190 matching lines @@
     port = new ReceivePort();
     testRead();
     testReadSync();
     testReadStream();
     testLength();
     testLengthSync();
     testPosition();
     testPositionSync();
     testOpenDirectoryAsFile();
     testOpenDirectoryAsFileSync();
+    testOpenFileFromPath();
     testReadAsBytes();
     testReadAsBytesSync();
     testReadAsText();
     testReadAsTextSync();
     testReadAsLines();
     testReadAsLinesSync();
     testReadAsErrors();
     testLastModified();
     testLastModifiedSync();
 
@@ skipping 17 matching lines @@
       testWriteVariousLists();
       testDirectory();
       testDirectorySync();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }