Disable tabs.relativeUrlTabsUpdate ran in ExtensionApiTest.Tabs until it beco...

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

 // tabs api test
 // browser_tests.exe --gtest_filter=ExtensionApiTest.Tabs
 
 // We have a bunch of places where we need to remember some state from one
 // test (or setup code) to subsequent tests.
 var firstWindowId = null;
 var secondWindowId = null;
 var firstTabIndex = null;
 var testTabId = null;
 
@@ skipping 330 matching lines @@
   // The subsequent three tests all load relative.html, which calls
   // this page's relativePageLoad(), which ends the test.
   function relativeUrlTabsCreate() {
     chrome.tabs.create({windowId: firstWindowId, url: 'relative.html'}, 
       function(tab){
         testTabId = tab.id;
       }
     );
   },
 
+  /* FIXME: Bug 21851. Make this test item not flaky.
   function relativeUrlTabsUpdate() {
     chrome.tabs.update(testTabId, {url: "chrome://a/"}, function(tab) {
       chrome.test.assertEq("chrome://a/", tab.url);
       chrome.tabs.update(tab.id, {url: "relative.html"}, function(tab) {  
       });
     });
-  },
+  }, */
   
   function relativeUrlWindowsCreate() {
     chrome.windows.create({url: "relative.html"});
   }
 
   // TODO(asargent) We still need to add tests for the following:
   //  Methods:
   //   -chrome.tabs.connect
   //  Events:
   //   -chrome.tabs.onAttached
   //   -chrome.tabs.onDetched
   //
   // Also, it would be an improvement to check the captureVisibleTab results
   // against a known-good result.
 ]);