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.

if (x === y) { 
    
    return x !== 0 || 1 / x === 1 / y;
  } else {
    
    return x !== x && y !== y;
  }
}
function createChainableTypeChecker(validate) {