[telemetry] Make single-benchmark measurements protected and undiscoverable.

tools/perf/benchmarks/blink_perf.js

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function() {
 window.testRunner = {};
 window.testRunner.isDone = false;
 
 testRunner.waitUntilDone = function() {};
 testRunner.dumpAsText = function() {};
 testRunner.notifyDone = function() {
   this.isDone = true;
 };
 
 window.GCController = {};
 
 GCController.collect = function() {
   gc();
 };
 })();