function AssertionError(messagePattern, messageArgs) {
  DebugError.call(this, subs(messagePattern, messageArgs));

  /**
   * The message pattern used to format the error message. Error handlers can
   * use this to uniquely identify the assertion.
   * @type {string}
   */
  this.messagePattern = messagePattern;
}
Error object for failed assertions.
@param {string} messagePattern The pattern that was used to form message.
@param {!Array<*>} messageArgs The items to substitute into the pattern.
@constructor
@extends {DebugError}
@final