Provide Point+Size, Point-Point, Point.toSize(), and Rect.toPoint().

sky/engine/core/painting/Size.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;
 
 /// Holds a 2D floating-point size.
+/// Think of this as a vector from Point(0,0) to Point(size.width, size.height)
 class Size {
   final double width;
   final double height;
 
   const Size(this.width, this.height);
 
   const Size.infinite() : width = double.INFINITY, height = double.INFINITY;
 
   const Size.fromWidth(this.width) : height = double.INFINITY;
   const Size.fromHeight(this.height) : width = double.INFINITY;
 
-  bool operator ==(other) {
-    if (!(other is Size)) return false;
-    return width == other.width && height == other.height;
-  }
+  bool operator ==(other) => other is Size && width == other.width && height == other.height;
+
+  // does the equivalent of "return new Point(0,0) + this"
+  Point toPoint() => new Point(this.width, this.height);
+
   int get hashCode {
     int result = 373;
     result = 37 * result + width.hashCode;
     result = 37 * result + height.hashCode;
     return result;
   }
   String toString() => "Size($width, $height)";
 }