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

chrome/test/data/devtools/extensions/devtools_messaging/background.js

 function onRequest(request, sender, callback) {
   var response = JSON.stringify(request);
   callback("onRequest callback: " + response);
 }
 
 chrome.extension.onRequest.addListener(onRequest);
 
 function onMessage(port, message) {
   port.postMessage("port.onMessage: " + message);
 }
 
 function onConnect(port) {
   port.onMessage.addListener(onMessage.bind(null, port));
 }
 
-chrome.extension.onConnect.addListener(onConnect);
+chrome.runtime.onConnect.addListener(onConnect);