Oilpan: fix build after r197958.

Source/modules/cachestorage/Cache.cpp

Index: Source/modules/cachestorage/Cache.cpp
diff --git a/Source/modules/cachestorage/Cache.cpp b/Source/modules/cachestorage/Cache.cpp
index 8a6d65ea6132c018f2bb19007a4ce6b435da63f5..bc3e950c758ba8c18ff00eccee5913b2ad3cbdbf 100644
--- a/Source/modules/cachestorage/Cache.cpp
+++ b/Source/modules/cachestorage/Cache.cpp
@@ -212,13 +212,14 @@ public:
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         visitor->trace(m_cache);
+        visitor->trace(m_resolver);
     }
 
 private:
     bool m_completed = false;
     int m_numberOfRemainingOperations;
     Member<Cache> m_cache;
-    RefPtrWillBePersistent<ScriptPromiseResolver> m_resolver;
+    RefPtrWillBeMember<ScriptPromiseResolver> m_resolver;
     Vector<WebServiceWorkerCache::BatchOperation> m_batchOperations;
 };