diff -r 000000000000 -r 6474c204b198 gfx/thebes/RoundedRect.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/thebes/RoundedRect.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * 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/. */
+
+#include "gfxRect.h"
+
+namespace mozilla {
+/* A rounded rectangle abstraction.
+ *
+ * This can represent a rectangle with a different pair of radii on each corner.
+ *
+ * Note: CoreGraphics and Direct2D only support rounded rectangle with the same
+ * radii on all corners. However, supporting CSS's border-radius requires the extra flexibility. */
+struct RoundedRect {
+    RoundedRect(gfxRect &aRect, gfxCornerSizes &aCorners) : rect(aRect), corners(aCorners) { }
+    void Deflate(gfxFloat aTopWidth, gfxFloat aBottomWidth, gfxFloat aLeftWidth, gfxFloat aRightWidth) {
+        // deflate the internal rect
+        rect.x += aLeftWidth;
+        rect.y += aTopWidth;
+        rect.width = std::max(0., rect.width - aLeftWidth - aRightWidth);
+        rect.height = std::max(0., rect.height - aTopWidth - aBottomWidth);
+
+        corners.sizes[NS_CORNER_TOP_LEFT].width  = std::max(0., corners.sizes[NS_CORNER_TOP_LEFT].width - aLeftWidth);
+        corners.sizes[NS_CORNER_TOP_LEFT].height = std::max(0., corners.sizes[NS_CORNER_TOP_LEFT].height - aTopWidth);
+
+        corners.sizes[NS_CORNER_TOP_RIGHT].width  = std::max(0., corners.sizes[NS_CORNER_TOP_RIGHT].width - aRightWidth);
+        corners.sizes[NS_CORNER_TOP_RIGHT].height = std::max(0., corners.sizes[NS_CORNER_TOP_RIGHT].height - aTopWidth);
+
+        corners.sizes[NS_CORNER_BOTTOM_LEFT].width  = std::max(0., corners.sizes[NS_CORNER_BOTTOM_LEFT].width - aLeftWidth);
+        corners.sizes[NS_CORNER_BOTTOM_LEFT].height = std::max(0., corners.sizes[NS_CORNER_BOTTOM_LEFT].height - aBottomWidth);
+
+        corners.sizes[NS_CORNER_BOTTOM_RIGHT].width  = std::max(0., corners.sizes[NS_CORNER_BOTTOM_RIGHT].width - aRightWidth);
+        corners.sizes[NS_CORNER_BOTTOM_RIGHT].height = std::max(0., corners.sizes[NS_CORNER_BOTTOM_RIGHT].height - aBottomWidth);
+    }
+    gfxRect rect;
+    gfxCornerSizes corners;
+};
+
+} // namespace mozilla