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

sky/examples/raw/hello_world.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";
-import 'dart:sky';
-
-Picture draw(int a, int r, int g, int b) {
-  double width = view.width;
-  double height = view.height;
-
-  PictureRecorder recorder = new PictureRecorder();
-  Canvas canvas = new Canvas(recorder, width, height);
-  double radius = min(width, height) * 0.45;
-
-  Paint paint = new Paint()..color = new Color.fromARGB(a, r, g, b);
-  canvas.drawCircle(width / 2, height / 2, radius, paint);
-  return recorder.endRecording();
-}
-
-bool handleEvent(Event event) {
-  if (event.type == "pointerdown") {
-    view.picture = draw(255, 0, 0, 255);
-    view.scheduleFrame();
-    return true;
-  }
-
-  if (event.type == "pointerup") {
-    view.picture = draw(255, 0, 255, 0);
-    view.scheduleFrame();
-    return true;
-  }
-
-  if (event.type == "back") {
-    print("Pressed back button.");
-    return true;
-  }
-
-  return false;
-}
-
-void main() {
-  print("Hello, world");
-  view.picture = draw(255, 0, 255, 0);
-  view.scheduleFrame();
-
-  view.setEventCallback(handleEvent);
-}