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

sky/examples/widgets/hello_widgets.dart

Index: sky/examples/widgets/hello_widgets.dart
diff --git a/sky/examples/widgets/hello_widgets.dart b/sky/examples/widgets/hello_widgets.dart
deleted file mode 100644
index 34c1f7e58479296fa1c6729be63260913646bf68..0000000000000000000000000000000000000000
--- a/sky/examples/widgets/hello_widgets.dart
+++ /dev/null
@@ -1,15 +0,0 @@
-// 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 'package:sky/widgets/basic.dart';
-
-class HelloWorldApp extends App {
-  Widget build() {
-    return new Text('Hello, widgets!');
-  }
-}
-
-void main() {
-  runApp(new HelloWorldApp());
-}