Add synchronous directory listing to dart:io Directory.

sdk/lib/io/directory_impl.dart

Index: sdk/lib/io/directory_impl.dart
diff --git a/sdk/lib/io/directory_impl.dart b/sdk/lib/io/directory_impl.dart
index a3f8c281cfd0bac2b6c04523b582ac1d8350246f..8017e956542258c0c1299fb7058163173488eeeb 100644
--- a/sdk/lib/io/directory_impl.dart
+++ b/sdk/lib/io/directory_impl.dart
@@ -26,6 +26,7 @@ class _Directory implements Directory {
   external static _create(String path);
   external static _delete(String path, bool recursive);
   external static _rename(String path, String newPath);
+  external static List _list(String path, bool recursive);
   external static SendPort _newServicePort();
 
   Future<bool> exists() {
@@ -229,6 +230,13 @@ class _Directory implements Directory {
     return new _DirectoryLister(_path, recursive);
   }
 
+  List listSync({bool recursive: false}) {
+    if (_path is! String || recursive is! bool) {
+      throw new ArgumentError();
+    }
+    return _list(_path, recursive);
+  }
+
   String get path => _path;
 
   String toString() => "Directory: '$path'";