Update cpu and memory metric calculation and several small improvements.

chrome/test/media_router/telemetry/benchmarks/pagesets/cpu_memory_script.js

 /**
  * Copyright 2016 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.
  *
  * @fileoverview Script to interact with test extension to get CPU/memory usage.
  *
  */
 
 
 // MR test extension ID.
 var extensionId = 'ocihafebdemjoofhbdnamghkfobfgbal';
 
 /**
  * The dictionary to store the performance results with the following format:
  * key: the metric, e.g. CPU, private memory
  * value: map of the performance results for different processes.
  *    key: process type, e.g. tab, browser, gpu, extension.
- *    value: list of the performance results.
+ *    value: list of the performance results per second. Task Manager notifies
+ *           the event listener nearly every second for the latest status of
+ *           each process.
  */
 window.perfResults = {};
 
 /**
  * Connects to the test extension and starts to collect CPU/memory usage data.
  */
 function collectPerfData() {
   processCpuPort_ = openPort_('collectData');
   if (processCpuPort_) {
     processCpuPort_.onMessage.addListener(function(message) {
@@ skipping 16 matching lines @@
 }
 
 function openPort_(name) {
   var rt = window.chrome.runtime;
   if (rt && rt.connect) {
     console.info('Opening port named ' + name);
     return rt.connect(extensionId, {'name': name});
   }
   return null;
 }