static void
AddTransformedRegion(nsIntRegion& aDest, const nsIntRegion& aSource, const Matrix4x4& aTransform)
{
  nsIntRegionRectIterator iter(aSource);
  const IntRect *r;
  while ((r = iter.Next())) {
    aDest.Or(aDest, TransformRect(*r, aTransform));
  }
  aDest.SimplifyOutward(20);
}
static void
AddRegion(nsIntRegion& aDest, const nsIntRegion& aSource)
{
  aDest.Or(aDest, aSource);
  aDest.SimplifyOutward(20);
}