function freeTile(tile) {
  if (defined(tile)) {
    tile.freeResources();
  }
}
Frees the resources associated with this tile and returns it to the <code>START</code>
{@link QuadtreeTileLoadState}.  If the {@link QuadtreeTile#data} property is defined and it
has a <code>freeResources</code> method, the method will be invoked.

@memberof QuadtreeTile