Add a new bindings2/scripts directory for Dart bindings

sky/engine/bindings2/scripts/templates/dart_blink.template

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// WARNING: Do not edit - generated code.
+library sky.core;
+
+import "dart:nativewrappers";
+
+{% for interface in interfaces %}
+part '{{interface.name}}.dart';
+{% endfor %}
+
+{% for callback in callbacks %}
+part '{{callback.name}}.dart';
+{% endfor %}
+
+Window window;
+Document get document => window.document;
+
+typedef EventListener(Event event);