Make tracing work in the new .dart world.

sky/engine/bindings/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 dart.sky;
 
 import "dart:nativewrappers";
 import 'dart:typed_data';
 
 {% 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;
 
+final Tracing tracing = new Tracing();
+
 View view;
 
 typedef EventListener(Event event);