Made index_db Cursor.next behavior consistent between JS and vm.

sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart

Index: sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
diff --git a/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart b/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
index 7ca47357ecaeab79dc049d954187d9acfe852878..ca20f438a6ac4ff056eabca407df76ab09773891 100644
--- a/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
+++ b/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
@@ -231,6 +231,15 @@ class Cursor extends Interceptor native "IDBCursor" {
     }
   }
 
+  @JSName('continue')
+  @DomName('IDBCursor.continue')
+  void next([Object key]) {
+    if (key == null) {
+      JS('void', '#.continue()', this);
+    } else {
+      JS('void', '#.continue(#)', this, key);
+    }
+  }
   
   @DomName('IDBCursor.direction')
   @DocsEditable()
@@ -263,11 +272,6 @@ class Cursor extends Interceptor native "IDBCursor" {
   @DocsEditable()
   Request _delete() native;
 
-  @JSName('continue')
-  @DomName('IDBCursor.continue')
-  @DocsEditable()
-  void next([Object key]) native;
-
   @DomName('IDBCursor.update')
   @DocsEditable()
   Request _update(/*any*/ value) {