Revert IDB optional mode parameter.

tests/html/indexeddb_3_test.dart

Index: tests/html/indexeddb_3_test.dart
diff --git a/tests/html/indexeddb_3_test.dart b/tests/html/indexeddb_3_test.dart
index 260cdd7ac20b5361fbdc2dbc68a599471fbbf8b9..436b12591897ef1d323778ac9dace6cd7592efca 100644
--- a/tests/html/indexeddb_3_test.dart
+++ b/tests/html/indexeddb_3_test.dart
@@ -75,7 +75,7 @@ class Test {
 
   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) {
@@ -89,7 +89,7 @@ class Test {
   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;
@@ -115,7 +115,7 @@ class Test {
   }
 
   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');