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.

function validate(props, propName, componentName, location, propFullName) {
    if (!isNode(props[propName])) {
      var locationName = ReactPropTypeLocationNames[location];
      return new Error(
        `Invalid ${locationName} \`${propFullName}\` supplied to ` +
        `\`${componentName}\`, expected a ReactNode.`
      );
    }
    return null;
  }
  return createChainableTypeChecker(validate);
}
function createShapeTypeChecker(shapeTypes) {
  function validate(props, propName, componentName, location, propFullName) {