Move sky/examples to sky/sdk/lib/example, and code changes to support that change. Fixes T277.

sky/tests/examples/stocks.dart

 // 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.
 
 import 'dart:async';
 
 import 'package:sky/widgets/widget.dart';
 
-import '../../examples/stocks2/lib/stock_app.dart';
+import '../../sdk/lib/example/stocks2/lib/stock_app.dart';
 import '../resources/display_list.dart';
 
 class TestStocksApp extends StocksApp {
 
   Completer _completer = new Completer();
   Future get isMounted => _completer.future;
 
   void didMount() {
     super.didMount();
     _completer.complete();
   }
 }
 
 main() async {
   TestRenderView testRenderView = new TestRenderView();
   TestStocksApp app = new TestStocksApp();
   runApp(app, renderViewOverride: testRenderView);
   await testRenderView.checkFrame();
   await app.isMounted;
   await testRenderView.checkFrame();
   testRenderView.endTest();
 }