static recastDictAsObject_(dict) {
    goog.asserts.assert(!(dict instanceof Map), 'dict should not be a map');
    return /** @type {!Object} */ (dict);
  }
Allows us to tell the compiler that the dictionary "map" is actually a
generic object, for backwards compatibility.
@param {!Map<string, Object>} dict
@return {!Object}
@suppress {invalidCasts}
@private