Mark DOMStringList.contains() as deprecated, add console warning.

LayoutTests/storage/indexeddb/resources/shared.js

 var jsTestIsAsync = true;
 if (self.importScripts && !self.postMessage) {
     // Shared worker.  Make postMessage send to the newest client, which in
     // our tests is the only client.
 
     // Store messages for sending until we have somewhere to send them.
     self.postMessage = function(message)
     {
         if (typeof self.pendingMessages === "undefined")
             self.pendingMessages = [];
@@ skipping 102 matching lines @@
     evalAndLog(cmd);
   }
   return callback;
 }
 
 // If this function is deleted, a standalone layout test exercising its
 // functionality should be added.
 function deleteAllObjectStores(db)
 {
     while (db.objectStoreNames.length)
-        db.deleteObjectStore(db.objectStoreNames.item(0));

[philipj_slow, 2015/03/06 03:03:49]

Can you leave one use of item() in the tests so that it can't accidentally
regress? That would also show that the deprecation message works as it should.

[jsbell, 2015/03/06 17:19:20]

Sure. The behavior of item() is covered in fast/dom/domstringlist.html but
that's a textharness.js-based test so the deprecation is not captured.

+        db.deleteObjectStore(db.objectStoreNames[0]);
     debug("Deleted all object stores.");
 }
 
 function setDBNameFromPath(suffix) {
     var name = self.location.pathname.substring(1 + self.location.pathname.lastIndexOf("/"));
     if (suffix)
         name += suffix;
     evalAndLog('dbname = "' + name + '"');
 }
 
@@ skipping 74 matching lines @@
 
     requests.forEach(function(req) {
         req.onsuccess = function() {
             --count;
             if (!count)
                 callback(requests);
         };
         req.onerror = unexpectedErrorCallback;
     });
 }