dart2js_html: Fix for issue 29538 - some returned lists may be null

sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart

 /**
  * A client-side key-value store with support for indexes.
  *
  * Many browsers support IndexedDB—a web standard for
  * an indexed database.
  * By storing data on the client in an IndexedDB,
  * a web app gets some advantages, such as faster performance and persistence.
  * To find out which browsers support IndexedDB,
  * refer to [Can I Use?](http://caniuse.com/#feat=indexeddb)
  *
@@ skipping 431 matching lines @@
   @DocsEditable()
   static const EventStreamProvider<VersionChangeEvent> versionChangeEvent =
       const EventStreamProvider<VersionChangeEvent>('versionchange');
 
   @DomName('IDBDatabase.name')
   @DocsEditable()
   final String name;
 
   @DomName('IDBDatabase.objectStoreNames')
   @DocsEditable()
-  @Returns('DomStringList')
+  @Returns('DomStringList|Null')
   @Creates('DomStringList')
   final List<String> objectStoreNames;
 
   @DomName('IDBDatabase.version')
   @DocsEditable()
   @Creates('int|String|Null')
   @Returns('int|String|Null')
   final Object version;
 
   @DomName('IDBDatabase.close')
@@ skipping 566 matching lines @@
   factory ObjectStore._() {
     throw new UnsupportedError("Not supported");
   }
 
   @DomName('IDBObjectStore.autoIncrement')
   @DocsEditable()
   final bool autoIncrement;
 
   @DomName('IDBObjectStore.indexNames')
   @DocsEditable()
-  @Returns('DomStringList')
+  @Returns('DomStringList|Null')
   @Creates('DomStringList')
   final List<String> indexNames;
 
   @DomName('IDBObjectStore.keyPath')
   @DocsEditable()
   @annotation_Creates_SerializedScriptValue
   final Object keyPath;
 
   @DomName('IDBObjectStore.name')
   @DocsEditable()
@@ skipping 367 matching lines @@
   @DocsEditable()
   final DomError error;
 
   @DomName('IDBTransaction.mode')
   @DocsEditable()
   final String mode;
 
   @DomName('IDBTransaction.objectStoreNames')
   @DocsEditable()
   @Experimental() // untriaged
-  @Returns('DomStringList')
+  @Returns('DomStringList|Null')
   @Creates('DomStringList')
   final List<String> objectStoreNames;
 
   @DomName('IDBTransaction.abort')
   @DocsEditable()
   void abort() native;
 
   @DomName('IDBTransaction.objectStore')
   @DocsEditable()
   ObjectStore objectStore(String name) native;
@@ skipping 59 matching lines @@
   @Creates('int|String|Null')
   @Returns('int|String|Null')
   final int newVersion;
 
   @DomName('IDBVersionChangeEvent.oldVersion')
   @DocsEditable()
   @Creates('int|String|Null')
   @Returns('int|String|Null')
   final int oldVersion;
 }