static unwrap(safeStyle) {
    // Perform additional Run-time type-checking to ensure that
    // safeStyle is indeed an instance of the expected type.  This
    // provides some additional protection against security bugs due to
    // application code that disables type checks.
    // Specifically, the following checks are performed:
    // 1. The object is an instance of the expected type.
    // 2. The object is not an instance of a subclass.
    if (safeStyle instanceof SafeStyle && safeStyle.constructor === SafeStyle) {
      return safeStyle.privateDoNotAccessOrElseSafeStyleWrappedValue_;
    } else {
      fail(
          `expected object of type SafeStyle, got '${safeStyle}` +
          '\' of type ' + goog.typeOf(safeStyle));
      return 'type_error:SafeStyle';
    }
  }
Performs a runtime check that the provided object is indeed a
SafeStyle object, and returns its value.

@param {!SafeStyle} safeStyle The object to extract from.
@return {string} The safeStyle object's contained string, unless
    the run-time type check fails. In that case, `unwrap` returns an
    innocuous string, or, if assertions are enabled, throws
    `AssertionError`.