static invokeSpy(spy, ...varArgs) {
    // TODO: There should be a way to alter the externs for jasmine.Spy so that
    // this utility is not needed.
    // Why isn't there something like ICallable in Closure?
    // https://github.com/shaka-project/closure-compiler/issues/946
    // Why isn't it enough that jasmine.Spy extends Function?
    // https://github.com/shaka-project/closure-compiler/issues/1422
    return /** @type {Function} */(spy)(...varArgs);
  }
@param {!jasmine.Spy} spy
@param {...*} varArgs
@return {*}