Have ScriptPromiseResolver on the Oilpan heap always.

Source/modules/background_sync/SyncRegistration.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "modules/background_sync/SyncRegistration.h"
 
 #include "bindings/core/v8/CallbackPromiseAdapter.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/DOMException.h"
@@ skipping 37 matching lines @@
 
 SyncRegistration::~SyncRegistration()
 {
 }
 
 ScriptPromise SyncRegistration::unregister(ScriptState* scriptState)
 {
     if (m_id == WebSyncRegistration::UNREGISTERED_SYNC_ID)
         return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(AbortError, "Operation failed - not a valid registration object"));
 
-    RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
+    ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = resolver->promise();
 
     WebSyncProvider* webSyncProvider = Platform::current()->backgroundSyncProvider();
     ASSERT(webSyncProvider);
 
     webSyncProvider->unregisterBackgroundSync(WebSyncRegistration::PeriodicityOneShot, m_id, m_tag, m_serviceWorkerRegistration->webRegistration(), new SyncUnregistrationCallbacks(resolver, m_serviceWorkerRegistration));
 
     return promise;
 }
 
 DEFINE_TRACE(SyncRegistration)
 {
     visitor->trace(m_serviceWorkerRegistration);
 }
 
 } // namespace blink