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 (!isNode(entry[1])) {
                return false;
              }
            }
          }
        }
      } else {
        return false;
      }
      return true;
    default:
      return false;
  }
}
function isSymbol(propType, propValue) {
  
  if (propType === 'symbol') {
    return true;
  }
  
  if (propValue['@@toStringTag'] === 'Symbol') {
    return true;
  }
  
  if (typeof Symbol === 'function' && propValue instanceof Symbol) {
    return true;
  }
  return false;
}
function getPropType(propValue) {