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

sky/examples/raw/shadow.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:sky';
-
-void beginFrame(double timeStamp) {
-  var size = 100.0;
-  PictureRecorder recorder = new PictureRecorder();
-  Canvas canvas = new Canvas(recorder, view.width, view.height);
-  canvas.translate(size + 10.0, size + 10.0);
-
-  Paint paint = new Paint();
-  paint.color = const Color.fromARGB(255, 0, 255, 0);
-  var builder = new LayerDrawLooperBuilder()
-    // Shadow layer.
-    ..addLayerOnTop(
-        new DrawLooperLayerInfo()
-          ..setPaintBits(PaintBits.all)
-          ..setOffset(const Point(5.0, 5.0))
-          ..setColorMode(TransferMode.src),
-        (Paint layerPaint) {
-      layerPaint.color = const Color.fromARGB(128, 55, 55, 55);
-      layerPaint.setMaskFilter(
-          new MaskFilter.blur(BlurStyle.normal, 5.0, highQuality: true));
-    })
-    // Main layer.
-    ..addLayerOnTop(new DrawLooperLayerInfo(), (Paint) {});
-  paint.setDrawLooper(builder.build());
-
-  canvas.drawPaint(
-      new Paint()..color = const Color.fromARGB(255, 255, 255, 255));
-  canvas.drawRect(new Rect.fromLTRB(-size, -size, size, size), paint);
-  view.picture = recorder.endRecording();
-}
-
-void main() {
-  view.setBeginFrameCallback(beginFrame);
-  view.scheduleFrame();
-}