Sky: different tack for custom Rect type in the Canvas API.

sky/engine/core/painting/Rect.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.
+
+part of dart.sky;
+
+class Rect {
+  Float32List _value;
+  double get left => _value[0];
+  double get top => _value[1];
+  double get right => _value[2];
+  double get bottom => _value[3];
+
+  void setLTRB(double left, double top, double right, double bottom) {
+    _value = new Float32List.fromList([left, top, right, bottom]);
+  }
+}