function assertIdle(dlg) {
  assertFalse(dlg.isDragging());
  assertNull('dragger element has been cleaned up', dlg.draggerEl_);
  assertNull('dragger has been cleaned up', dlg.dragger_);
  assertEquals(
      'the additional event listeners have been removed', initialListenerCount,
      googObject.getCount(dlg.eventHandler_.keys_));
}
Asserts that the DragListGroup is in idle state.
@param {!DragListGroup} dlg The DragListGroup to examine.
@suppress {visibility} suppression added to enable type checking