Rewrite BrowserTest.PageLanguageDetection to use a new tab instead of the one with about:blank.

chrome/test/data/extensions/api_test/tabs/basics/crud.html

 <script src="tabs_util.js"></script>
 
 <script>
 var firstWindowId;
 
 chrome.test.runTests([
   function getSelected() {
     chrome.tabs.getSelected(null, pass(function(tab) {
       assertEq(location.href, tab.url);
       assertEq(location.href, tab.title);
@@ skipping 74 matching lines @@
     }));
   },
 
   function getAllInWindowNullArg() {
     chrome.tabs.getAllInWindow(null, pass(function(tabs) {
       assertEq(5, tabs.length);
       assertEq(firstWindowId, tabs[0].windowId);
     }));
   },
 
-  /* Sadly, this has also regressed. crbug.com/60802.
   function detectLanguage() {
     chrome.tabs.getAllInWindow(firstWindowId, pass(function(tabs) {
       chrome.tabs.detectLanguage(tabs[0].id, pass(function(lang) {
-        assertEq("en", lang);
+        assertEq("und", lang);
       }));
     }));
   },
-  */
 
   function windowCreate() {
     chrome.windows.create({type: "popup"}, pass(function(window) {
       assertEq("popup", window.type);
       assertTrue(!window.incognito);
     }));
     chrome.windows.create({incognito: true}, pass(function(window) {
       // This extension is not incognito-enabled, so it shouldn't be able to
       // see the incognito window.
       assertEq(null, window);
     }));
   },
 
   /* Disabled -- see http://bugs.chromium.org/58229.
   function windowSetFocused() {
     chrome.windows.getCurrent(function(oldWin) {
       chrome.windows.create({}, function(newWin) {
         assertTrue(newWin.focused);
         chrome.windows.update(oldWin.id, {focused:true});
         chrome.windows.get(oldWin.id, pass(function(oldWin2) {
           assertTrue(oldWin2.focused);
         }));
       });
     });
   },
   */
 ]);
 </script>