function setErrorPredicate(pred) {
  this._errorPredicate = pred
}
Sets a function to call when an error is noticed to determine if it is really
an error.

@memberof WebFrameworkShim.prototype
@param {function(object): boolean} pred
 Function which should return true if the object passed to it is considered
 an error.
@see WebFrameworkShim#noticeError
@see WebFrameworkShim#errorHandled