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

sky/engine/core/painting/Color.dart

Index: sky/engine/core/painting/Color.dart
diff --git a/sky/engine/core/painting/Color.dart b/sky/engine/core/painting/Color.dart
index 5789e40e653c8e75268699279296a0b9548b5c21..0ea9fa98063b04f72b28f81c733c91f4f9d3110f 100644
--- a/sky/engine/core/painting/Color.dart
+++ b/sky/engine/core/painting/Color.dart
@@ -16,6 +16,7 @@ class Color {
               ((b & 0xff) << 0));
 
   bool operator ==(other) => other is Color && _value == other._value;
+
   int get hashCode => _value.hashCode;
   String toString() => "Color(0x${_value.toRadixString(16).padLeft(8, '0')})";
 }