src/render/context.js
function getChildContext (componentPrototype, instance, context) {
  if (componentPrototype.childContextTypes) {
    return assign(Object.create(null), context, instance.getChildContext());
  }
  return context;
}
function getChildContext (componentPrototype, instance, context) {
  if (componentPrototype.childContextTypes) {
    return assign(Object.create(null), context, instance.getChildContext());
  }
  return context;
}
function getChildContext ( componentPrototype , instance , context ) { if ( componentPrototype . childContextTypes ) { return assign ( Object . create ( null ) , context , instance . getChildContext ( ) ) ; } return context ; }
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.
Using a component prototype s childContextTypes generate an object that will merged into the master traversal context for that component s subtree .