Refactor BeforeInstallPromptEvent to use ScriptPromiseProperty

Source/modules/app_banner/AppBannerCallbacks.h

Index: Source/modules/app_banner/AppBannerCallbacks.h
diff --git a/Source/modules/app_banner/AppBannerCallbacks.h b/Source/modules/app_banner/AppBannerCallbacks.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4a3baa75aaebafd21083980632500ed41b94681
--- /dev/null
+++ b/Source/modules/app_banner/AppBannerCallbacks.h
@@ -0,0 +1,27 @@
+// 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 AppBannerCallbacks_h
+#define AppBannerCallbacks_h
+
+#include "modules/app_banner/BeforeInstallPromptEvent.h"
+#include "public/platform/modules/app_banner/WebAppBannerClient.h"
+
+namespace blink {
+
+class AppBannerCallbacks : public WebAppBannerCallbacks {
+public:
+    explicit AppBannerCallbacks(UserChoiceProperty*);
+    ~AppBannerCallbacks() override = default;
+
+    // WebAppBannerCallbacks overrides.
+    void onSuccess(WebAppBannerPromptResult*) override;
+
+private:
+    Persistent<UserChoiceProperty> m_userChoice;
+};
+
+} // namespace blink
+
+#endif // AppBannerCallbacks_h