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

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

 function output(msg) {
   chrome.devtools.inspectedWindow.eval("console.log(unescape('" +
       escape(msg) + "'));")
 }
 
 var hadErrors = false;
 
 function assertEquals(expected, actual) {
   if (expected === actual)
     return;
@@ skipping 20 matching lines @@
     assertEquals('onRequest callback: ' + JSON.stringify(object), response);
     step3();
   });
 }
 
 function step3() {
   function onMessage(message) {
     assertEquals("port.onMessage: foo", message);
     completeTest();
   }
-  var port = chrome.extension.connect();
+  var port = chrome.runtime.connect();
   port.onMessage.addListener(onMessage);
   port.postMessage("foo");
 }
 
 step1();