Add support for transforms to container

sky/examples/raw/transform.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' as sky;
+import 'package:sky/framework/app.dart';
+import 'package:sky/framework/rendering/flex.dart';
+import 'package:sky/framework/rendering/box.dart';
+import 'package:vector_math/vector_math.dart';
+
+AppView app;
+
+void main() {
+  RenderDecoratedBox green = new RenderDecoratedBox(
+      decoration: new BoxDecoration(backgroundColor: 0xFF00FF00));
+  RenderSizedBox box = new RenderSizedBox(
+      desiredSize: new sky.Size(200.0, 200.0), child: green);
+
+  Matrix4 transform = new Matrix4.identity();
+  RenderTransform spin = new RenderTransform(
+      transform: transform, child: box);
+  spin.rotateZ(1.0);
+
+  RenderFlex flex = new RenderFlex();
+  flex.add(spin);
+  app = new AppView(flex);
+}