diff -r 000000000000 -r 6474c204b198 gfx/2d/BaseSize.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/2d/BaseSize.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,88 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_GFX_BASESIZE_H_
+#define MOZILLA_GFX_BASESIZE_H_
+
+#include "mozilla/Attributes.h"
+
+namespace mozilla {
+namespace gfx {
+
+/**
+ * Do not use this class directly. Subclass it, pass that subclass as the
+ * Sub parameter, and only use that subclass. This allows methods to safely
+ * cast 'this' to 'Sub*'.
+ */
+template <class T, class Sub>
+struct BaseSize {
+  T width, height;
+
+  // Constructors
+  MOZ_CONSTEXPR BaseSize() : width(0), height(0) {}
+  MOZ_CONSTEXPR BaseSize(T aWidth, T aHeight) : width(aWidth), height(aHeight) {}
+
+  void SizeTo(T aWidth, T aHeight) { width = aWidth; height = aHeight; }
+
+  bool IsEmpty() const {
+    return width == 0 || height == 0;
+  }
+
+  // Note that '=' isn't defined so we'll get the
+  // compiler generated default assignment operator
+
+  bool operator==(const Sub& aSize) const {
+    return width == aSize.width && height == aSize.height;
+  }
+  bool operator!=(const Sub& aSize) const {
+    return width != aSize.width || height != aSize.height;
+  }
+  bool operator<=(const Sub& aSize) const {
+    return width <= aSize.width && height <= aSize.height;
+  }
+  bool operator<(const Sub& aSize) const {
+    return *this <= aSize && *this != aSize;
+  }
+
+  Sub operator+(const Sub& aSize) const {
+    return Sub(width + aSize.width, height + aSize.height);
+  }
+  Sub operator-(const Sub& aSize) const {
+    return Sub(width - aSize.width, height - aSize.height);
+  }
+  Sub& operator+=(const Sub& aSize) {
+    width += aSize.width;
+    height += aSize.height;
+    return *static_cast<Sub*>(this);
+  }
+  Sub& operator-=(const Sub& aSize) {
+    width -= aSize.width;
+    height -= aSize.height;
+    return *static_cast<Sub*>(this);
+  }
+
+  Sub operator*(T aScale) const {
+    return Sub(width * aScale, height * aScale);
+  }
+  Sub operator/(T aScale) const {
+    return Sub(width / aScale, height / aScale);
+  }
+  void Scale(T aXScale, T aYScale) {
+    width *= aXScale;
+    height *= aYScale;
+  }
+
+  Sub operator*(const Sub& aSize) const {
+    return Sub(width * aSize.width, height * aSize.height);
+  }
+  Sub operator/(const Sub& aSize) const {
+    return Sub(width / aSize.width, height / aSize.height);
+  }
+};
+
+}
+}
+
+#endif /* MOZILLA_GFX_BASESIZE_H_ */