[AppBanner] Blink implementation of an event when an install banner is shown.

Source/modules/app_banner/BeforeInstallPromptEvent.h

Index: Source/modules/app_banner/BeforeInstallPromptEvent.h
diff --git a/Source/modules/app_banner/BeforeInstallPromptEvent.h b/Source/modules/app_banner/BeforeInstallPromptEvent.h
new file mode 100644
index 0000000000000000000000000000000000000000..23160ddde8b667d27b8923db7beb9e04c1a6cd23
--- /dev/null
+++ b/Source/modules/app_banner/BeforeInstallPromptEvent.h
@@ -0,0 +1,53 @@
+// 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 "modules/EventModules.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class BeforeInstallPromptEventInit;
+
+class BeforeInstallPromptEvent final : public Event {
+    DEFINE_WRAPPERTYPEINFO();
+public:
+    virtual ~BeforeInstallPromptEvent();
+
+    // For EventModules.cpp
+    static PassRefPtrWillBeRawPtr<BeforeInstallPromptEvent> create()
+    {
+        return adoptRefWillBeNoop(new BeforeInstallPromptEvent());
+    }
+
+    static PassRefPtrWillBeRawPtr<BeforeInstallPromptEvent> create(const AtomicString& name, const String& platform)
+    {
+        return adoptRefWillBeNoop(new BeforeInstallPromptEvent(name, platform));
+    }
+
+    static PassRefPtrWillBeRawPtr<BeforeInstallPromptEvent> create(const AtomicString& name, const BeforeInstallPromptEventInit& init)
+    {
+        return adoptRefWillBeNoop(new BeforeInstallPromptEvent(name, init));
+    }
+
+    String platform() const;
+    ScriptPromise userChoice(ScriptState*) const;
+
+    virtual const AtomicString& interfaceName() const override;
+
+private:
+    BeforeInstallPromptEvent();
+    BeforeInstallPromptEvent(const AtomicString& name, const String& platform);
+    BeforeInstallPromptEvent(const AtomicString& name, const BeforeInstallPromptEventInit&);
+
+    String m_platform;
+};
+
+DEFINE_TYPE_CASTS(BeforeInstallPromptEvent, Event, event, event->interfaceName() == EventNames::BeforeInstallPromptEvent, event.interfaceName() == EventNames::BeforeInstallPromptEvent);
+
+} // namespace blink
+
+#endif // BeforeInstallPromptEvent_h