Revert IDB optional mode parameter.

tests/html/indexeddb_4_test.dart

 library IndexedDB4Test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 import 'dart:indexed_db';
 
 // Test for KeyRange and Cursor.
 
 const String DB_NAME = 'Test';
 const String STORE_NAME = 'TEST';
@@ skipping 55 matching lines @@
   }
 
   _createAndOpenDb(afterOpen()) {
     var request = window.indexedDB.deleteDatabase(DB_NAME);
     request.onSuccess.listen(expectAsync1((e) { _openDb(afterOpen); }));
     request.onError.listen(fail('delete old Db'));
   }
 
   writeItems(int index) {
     if (index < 100) {
-      var transaction = db.transaction([STORE_NAME], mode : 'readwrite');
+      var transaction = db.transaction([STORE_NAME], 'readwrite');
       var request = transaction.objectStore(STORE_NAME)
           .put('Item $index', index);
       request.onSuccess.listen(expectAsync1((e) {
           writeItems(index + 1);
         }
       ));
       request.onError.listen(fail('put'));
     }
   }
 
   setupDb() { _createAndOpenDb(() => writeItems(0)); }
 
   testRange(range, expectedFirst, expectedLast) {
-    Transaction txn = db.transaction(STORE_NAME, mode : 'readonly');
+    Transaction txn = db.transaction(STORE_NAME, 'readonly');
     ObjectStore objectStore = txn.objectStore(STORE_NAME);
     Request cursorRequest = objectStore.openCursor(range);
     int itemCount = 0;
     int firstKey = null;
     int lastKey = null;
     cursorRequest.onSuccess.listen(expectAsync1((e) {
       var cursor = e.target.result;
       if (cursor != null) {
         if (firstKey == null) firstKey = cursor.key;
         lastKey = cursor.key;
@@ skipping 74 matching lines @@
     test('upper2', test_.upper2);
     test('upper3', test_.upper3);
 
     test('bound1', test_.bound1);
     test('bound2', test_.bound2);
     test('bound3', test_.bound3);
     test('bound4', test_.bound4);
     test('bound5', test_.bound5);
   }
 }