Update references to the extension messaging APIs to point to the "runtime"

tools/page_cycler/webpagereplay/extension/background.js

 // Copyright (c) 2012 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.
 
 // start.js sends a "start" message to set this.
 window.benchmarkConfiguration = {};
 
 // The callback (e.g. report writer) is set via AddBenchmarckCallback.
 window.benchmarkCallback;
 
@@ skipping 300 matching lines @@
     window.timeout = 40000;
     window.retries = 2;
   } else {
     window.iterations = benchmarkConfiguration["iterations"] || 3;
   }
   var sessionLoader = new SessionLoader(benchmarkCallback);
   console.log("pageSets: " + JSON.stringify(benchmarkConfiguration.pageSets));
   sessionLoader.run();
 }
 
-chrome.extension.onConnect.addListener(function(port) {
+chrome.runtime.onConnect.addListener(function(port) {
   port.onMessage.addListener(function(data) {
     if (data.message == "start") {
       window.benchmarkConfiguration = data.benchmark;
       Run()
     }
   });
-});
+});