Fix a memory leak in the app banner prompt layout tests.

Source/modules/app_banner/BeforeInstallPromptEvent.h

 // 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.
 
 #ifndef BeforeInstallPromptEvent_h
 #define BeforeInstallPromptEvent_h
 
 #include "bindings/core/v8/ScriptPromise.h"
+#include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "modules/EventModules.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class BeforeInstallPromptEventInit;
 class WebAppBannerClient;
 
 class BeforeInstallPromptEvent final : public Event {
     DEFINE_WRAPPERTYPEINFO();
@@ skipping 22 matching lines @@
     virtual const AtomicString& interfaceName() const override;
 
     ScriptPromise prompt(ScriptState*);
 
 private:
     BeforeInstallPromptEvent();
     BeforeInstallPromptEvent(const AtomicString& name, const Vector<String>& platforms, int requestId, WebAppBannerClient*);
     BeforeInstallPromptEvent(const AtomicString& name, const BeforeInstallPromptEventInit&);
 
     Vector<String> m_platforms;
-    ScriptPromise m_userChoice;
+    RefPtrWillBeMember<ScriptPromiseResolver> m_resolver;
 
     int m_requestId;
     WebAppBannerClient* m_client;
     bool m_redispatched;
 };
 
 DEFINE_TYPE_CASTS(BeforeInstallPromptEvent, Event, event, event->interfaceName() == EventNames::BeforeInstallPromptEvent, event.interfaceName() == EventNames::BeforeInstallPromptEvent);
 
 } // namespace blink
 
 #endif // BeforeInstallPromptEvent_h