code: function(context) {
      var maskedContext = this._maskContext(context);
      if ("production" !== process.env.NODE_ENV) {
        var Component = ReactNativeComponent.getComponentClassForElement(
          this._currentElement
        );
        if (Component.contextTypes) {
          this._checkPropTypes(
            Component.contextTypes,
            maskedContext,
            ReactPropTypeLocations.context
          );
        }
      }
      return maskedContext;
    }
docs: Filters the context object to only contain keys specified in
  `contextTypes`, and asserts that they are valid.
  
  @param {object} context
  @return {?object}
  @private