Oilpan: Ensure that classes with virtual trace methods always have vtables for their left-most base…

Source/modules/indexeddb/IndexedDBClient.h

Index: Source/modules/indexeddb/IndexedDBClient.h
diff --git a/Source/modules/indexeddb/IndexedDBClient.h b/Source/modules/indexeddb/IndexedDBClient.h
index c1010e8b666d34febdb95962ff6de4daa0195d2e..0c0ce39809ea23743355c95a21b111730e69ba29 100644
--- a/Source/modules/indexeddb/IndexedDBClient.h
+++ b/Source/modules/indexeddb/IndexedDBClient.h
@@ -38,7 +38,7 @@ class ExecutionContext;
 class IndexedDBClient : public GarbageCollected<IndexedDBClient> {
 public:
     static IndexedDBClient* create();
-    void trace(Visitor*) { }
+    virtual void trace(Visitor*) { }
 
     virtual bool allowIndexedDB(ExecutionContext*, const String& name) = 0;
 };