function toSize(size, dest) {
  if (Array.isArray(size)) {
    return size;
  }
  if (dest === undefined) {
    dest = [size, size];
  } else {
    dest[0] = size;
    dest[1] = size;
  }
  return dest;
}
Returns an `Size` array for the passed in number (meaning: square) or
`Size` array.
(meaning: non-square),
@param {number|Size} size Width and height.
@param {Size} [dest] Optional reusable size array.
@return {Size} Size.
@api