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

sky/engine/core/painting/Canvas.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.
-
-// This extends the Canvas.dart generated from Canvas.idl.
-
-class Rect {
-  List<double> _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 = [left, top, right, bottom];
-  }
-}
-
-class Canvas extends _Canvas {
-  double get height => _height;
-  double get width => _width;
-
-  void save() => _save();
-  void saveLayer(Rect bounds, Paint paint) =>
-      _saveLayer(bounds._value, Paint paint);
-  void restore() => _restore();
-  void translate(double dx, double dy) => _translate(dx, dy);
-  void scale(double sx, double sy) => _scale(sx, sy);
-  void rotateDegrees(double degrees) => _rotateDegrees(degrees);
-  void skew(double sx, double sy) => _skew(sx, sy);
-  void concat(List<double> matrix9) => _concat(matrix9);
-  void clipRect(Rect rect) => _clipRect(rect._value);
-
-  void drawPicture(Picture picture) => _drawPicture(picture);
-  void drawPaint(Paint paint) => _drawPaint(paint);
-  void drawRect(Rect rect, Paint paint) => _drawRect(rect._value, paint);
-  void drawOval(Rect rect, Paint paint) => _drawOval(rect._value, paint);
-  void drawCircle(double x, double y, double radius, Paint paint) =>
-      _drawCircle(x, y, radius, paint);
-}