code: function getChildContext (componentPrototype, instance, context) {
    if (componentPrototype.childContextTypes) {
      return assign(Object.create(null), context, instance.getChildContext());
    }
    return context;
  }
docs: Using a component prototype's `childContextTypes`, generate an
  object that will merged into the master traversal context for
  that component's subtree.
  
  @param      {Component}  componentPrototype  The component prototype.
  @param      {component}  instance            Component instance.
  @param      {Object}     context             The master context propagating through
  the traversal.
  
  @return     {Object}                         Child context merged into master context.