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

sky/sdk/lib/example/rendering/sector_layout.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:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/sky_binding.dart';
@@ skipping 520 matching lines @@
   stack.add(new RenderSolidColor(const Color(0xFFFFFF00), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFFFF9000), desiredDeltaRadius: 20.0));
   stack.add(new RenderSolidColor(const Color(0xFF00FF00)));
   rootCircle.add(stack);
   return new RenderBoxToRenderSectorAdapter(innerRadius: 50.0, child: rootCircle);
 }
 
 void main() {
   new SkyBinding(root: buildSectorExample());
 }