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) {
    var propValue = props[propName];
    var propType = getPropType(propValue);
    if (propType !== expectedType) {
      var locationName = ReactPropTypeLocationNames[location];
      
      
      
      var preciseType = getPreciseType(propValue);
      return new Error(
        `Invalid ${locationName} \`${propFullName}\` of type ` +
        `\`${preciseType}\` supplied to \`${componentName}\`, expected ` +
        `\`${expectedType}\`.`
      );
    }
    return null;
  }
  return createChainableTypeChecker(validate);
}
function createAnyTypeChecker() {
  return createChainableTypeChecker(emptyFunction.thatReturns(null));
}
function createArrayOfTypeChecker(typeChecker) {
  function validate(props, propName, componentName, location, propFullName) {