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

chrome/test/data/extensions/api_test/tabs/connect/echo.js

 // Content script that echoes back all messages.
 // Posting a message with "GET" returns the name and # of connections opened.
 var connections = 0;
 
-chrome.extension.onConnect.addListener(function onConnect(port) {
+chrome.runtime.onConnect.addListener(function onConnect(port) {
   connections++;
   port.onMessage.addListener(function onMessage(msg) {
     if (msg == "GET") {
       port.postMessage({"name": port.name, "connections": connections});
     } else {
       port.postMessage(msg);
     }
   });
 });
 
 chrome.extension.onRequest.addListener(function(request, sender, respond) {
   respond(request);
 });