Add support for file URIs and extracting the file path from file URIs

runtime/lib/uri_patch.dart

Index: runtime/lib/uri_patch.dart
diff --git a/runtime/lib/uri_patch.dart b/runtime/lib/uri_patch.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b07946d190d276da4dabe4f85cd104a1e05475a5
--- /dev/null
+++ b/runtime/lib/uri_patch.dart
@@ -0,0 +1,12 @@
+// 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.
+
+// VM implementation of Uri.
+patch class Uri {
+  static final bool _isWindowsCached = _isWindowsPlatform;
+
+  static bool get _isWindowsPlatform native "Uri_isWindowsPlatform";
+
+  /* patch */ static bool get _isWindows => _isWindowsCached;
+}