Split Size into Size and Offset.

sky/engine/core/painting/OffsetBase.dart

Index: sky/engine/core/painting/OffsetBase.dart
diff --git a/sky/engine/core/painting/OffsetBase.dart b/sky/engine/core/painting/OffsetBase.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1f5a0cb5c90216e75d9598a2c8d6461d7151ad0a
--- /dev/null
+++ b/sky/engine/core/painting/OffsetBase.dart
@@ -0,0 +1,28 @@
+// 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;
+
+abstract class OffsetBase {
+  const OffsetBase(this._dx, this._dy);
+
+  final double _dx;
+  final double _dy;
+
+  bool get isInfinite => _dx >= double.INFINITY || _dy >= double.INFINITY;
+
+  bool operator ==(other) {
+    return other is OffsetBase &&
+           other.runtimeType == runtimeType &&
+           other._dx == _dx &&
+           other._dy == _dy;
+  }
+
+  int get hashCode {
+    int result = 373;
+    result = 37 * result + _dx.hashCode;
+    result = 37 * result + _dy.hashCode;
+    return result;
+  }
+}