code: function getContext (componentPrototype, context) {
    if (componentPrototype.contextTypes) {
      const contextTypes = componentPrototype.contextTypes;
      return keys(context).reduce(
        (memo, contextKey) => {
          if (contextKey in contextTypes) {
            memo[contextKey] = context[contextKey];
          }
          return memo;
        },
        Object.create(null)
      );
    }
    return EMPTY_CONTEXT;
  }
docs: Using a component prototype's `contextTypes`, generate an object that
  will be used as React context for a component instance.
  
  @param      {Component}  componentPrototype  The component prototype.
  @param      {Object}     context             The master context propagating through
  traversal.
  
  @return     {Object}                         The generated context object.