Builds the content and label for a block.
For cacheable blocks, this is called during #pre_render.
$element: A renderable array.
A renderable array.
function _block_get_renderable_block($element) {
  $block = $element['#block'];
  // Don't bother to build blocks that aren't accessible.
  if ($element['#access'] = $block
    ->access()) {
    $element += entity_view($block, 'block');
  }
  return $element;
}