1. protected
  2. mustCallSuper
void dropChild(@checked AbstractNode child)

Disconnect the given node from this node.

Subclasses should call this function when they lose a child.

Source 

@protected
@mustCallSuper
void dropChild(@checked AbstractNode child) {
  assert(child != null);
  assert(child._parent == this);
  assert(child.attached == attached);
  child._parent = null;
  if (attached)
    child.detach();
}