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

chrome/test/data/extensions/browsertest/last_error/bg.js

 // Copyright (c) 2011 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.
 
 function fail() {
   window.domAutomationController.send(false);
   throw "Failed!";
 }
 
 function succeed() {
@@ skipping 18 matching lines @@
       for (var j = 0; j < win.tabs.length; j++) {
         var tab = win.tabs[j];
         if (tab.id > maxTabId)
           maxTabId = tab.id;
       }
     }
 
     // Now ask for the next highest tabId.
     chrome.tabs.get(maxTabId + 1, function(tab) {
       // Make sure lastError *is* set and tab is not.
-      if (!chrome.extension.lastError ||
-          !chrome.extension.lastError.message ||
+      if (!chrome.runtime.lastError ||
+          !chrome.runtime.lastError.message ||
           tab)
         fail();
 
       window.setTimeout(finish, 10);
     });
   });
 }
 
 function finish() {
   // Now make sure lastError is unset outside the callback context.
   if (chrome.tabs.lastError)
     fail();
 
   succeed();
 }
 
 document.documentElement.addEventListener("click", function() {
   testLastError();
 }, true);