function computeRectIntersection(rect1, rect2) {
  var top = Math.max(rect1.top, rect2.top);
  var bottom = Math.min(rect1.bottom, rect2.bottom);
  var left = Math.max(rect1.left, rect2.left);
  var right = Math.min(rect1.right, rect2.right);
  var width = right - left;
  var height = bottom - top;

  return (width >= 0 && height >= 0) && {
    top: top,
    bottom: bottom,
    left: left,
    right: right,
    width: width,
    height: height
  };
}
Returns the intersection between two rect objects.
@param {Object} rect1 The first rect.
@param {Object} rect2 The second rect.
@return {?Object} The intersection rect or undefined if no intersection
    is found.