Right now we validate some of our proptype definitions, but we don't surface the issue until that component class is consumed. We should instead validate these, in `__DEV__` only as warnings when the class in created. This means that a call to `React.PropTypes.onOf('foo')` results in an immediate warning logged.

This is a relatively contained bit of code so would be a good candidate for somebody looking to start contributing to React.

*    },
 *    render: function() {...}
 *  });
 *
 * @internal
 */
var ANONYMOUS = '<<anonymous>>';
var ReactPropTypes = {
  array: createPrimitiveTypeChecker('array'),
  bool: createPrimitiveTypeChecker('boolean'),
  func: createPrimitiveTypeChecker('function'),
  number: createPrimitiveTypeChecker('number'),
  object: createPrimitiveTypeChecker('object'),
  string: createPrimitiveTypeChecker('string'),
  symbol: createPrimitiveTypeChecker('symbol'),
  any: createAnyTypeChecker(),
  arrayOf: createArrayOfTypeChecker,
  element: createElementTypeChecker(),
  instanceOf: createInstanceTypeChecker,
  node: createNodeChecker(),
  objectOf: createObjectOfTypeChecker,
  oneOf: createEnumTypeChecker,
  oneOfType: createUnionTypeChecker,
  shape: createShapeTypeChecker,
};
/**
 * inlined Object.is polyfill to avoid requiring consumers ship their own
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
 */
function is(x, y) {