Revert IDB optional mode parameter.

tests/html/indexeddb_3_test.dart

 library IndexedDB3Test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 import 'dart:indexed_db';
 
 // Read with cursor.
 
 const String DB_NAME = 'Test';
 const String STORE_NAME = 'TEST';
@@ skipping 57 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)); }
 
   readAllViaCursor() {
-    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();
     int itemCount = 0;
     int sumKeys = 0;
     int lastKey = null;
     cursorRequest.onSuccess.listen(expectAsync1((e) {
       var cursor = e.target.result;
       if (cursor != null) {
         lastKey = cursor.key;
         itemCount += 1;
         sumKeys += cursor.key;
         window.console.log('${cursor.key}  ${cursor.value}');
         expect(cursor.value, 'Item ${cursor.key}');
         cursor.continueFunction();
       } else {
         // Done
         expect(lastKey, 99);
         expect(itemCount, 100);
         expect(sumKeys, (100 * 99) ~/ 2);
       }
     }, count:101));
     cursorRequest.onError.listen(fail('openCursor'));
   }
 
   readAllReversedViaCursor() {
-    Transaction txn = db.transaction(STORE_NAME, mode : 'readonly');
+    Transaction txn = db.transaction(STORE_NAME, 'readonly');
     ObjectStore objectStore = txn.objectStore(STORE_NAME);
     // TODO: create a KeyRange(0,100)
     Request cursorRequest = objectStore.openCursor(null, 'prev');
     int itemCount = 0;
     int sumKeys = 0;
     int lastKey = null;
     cursorRequest.onSuccess.listen(expectAsync1((e) {
       var cursor = e.target.result;
       if (cursor != null) {
         lastKey = cursor.key;
@@ skipping 17 matching lines @@
 
   // Don't bother with these tests if it's unsupported.
   // Support is tested in indexeddb_1_test
   if (IdbFactory.supported) {
     var test_ = new Test();
     test('prepare', test_.setupDb);
     test('readAll1', test_.readAllViaCursor);
     test('readAll2', test_.readAllReversedViaCursor);
   }
 }