Add deletion test, cursor read with writeback to same store.

chrome/test/data/indexeddb/perf_shared.js

 // Copyright (c) 2012 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.
 
 window.indexedDB = window.indexedDB || window.webkitIndexedDB ||
     window.mozIndexedDB || window.msIndexedDB;
 window.IDBKeyRange = window.IDBKeyRange || window.webkitIDBKeyRange;
 
 var automation = {
   results: {}
@@ skipping 314 matching lines @@
   }
   var oos;
   if (outputObjectStoreName)
     oos = transaction.objectStore(outputObjectStoreName);
   var numReadsLeft = numReads;
   request.onsuccess = function(event) {
     var cursor = event.target.result;
     if (cursor) {
       assert(numReadsLeft);
       --numReadsLeft;
-      if (oos) // Put in random order for maximum difficulty.
-        oos.put(cursor.value, Math.random());
+      if (oos)
+        // Put in random order for maximum difficulty.  We add in numKeys just
+        // in case we're writing back to the same store; this way we won't
+        // affect the number of keys available to the cursor, since we're always
+        // outside its range.
+        oos.put(cursor.value, numKeys + Math.random());
       values.push({key: cursor.key, value: cursor.value});
       cursor.continue();
     } else {
       assert(!numReadsLeft);
     }
   }
   request.onerror = onError;
 }