LibWeb: Add WebSocket bindings

The WebSocket bindings match the original specification from the
WHATWG living standard, but do not match the later update of the
standard that involves FETCH. The FETCH update will be handled later
since the changes would also affect XMLHttpRequest.

Userland/Libraries/LibWeb/HTML/CloseEvent.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2021, Dex♪ <dexes.ttp@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/DOM/Event.h>
+
+namespace Web::HTML {
+
+class CloseEvent : public DOM::Event {
+public:
+    using WrapperType = Bindings::CloseEventWrapper;
+
+    static NonnullRefPtr<CloseEvent> create(const FlyString& event_name, bool was_clean, u16 code, const String& reason)
+    {
+        return adopt_ref(*new CloseEvent(event_name, was_clean, code, reason));
+    }
+
+    virtual ~CloseEvent() override = default;
+
+    bool was_clean() { return m_was_clean; }
+    u16 code() const { return m_code; }
+    String reason() const { return m_reason; }
+
+protected:
+    CloseEvent(const FlyString& event_name, bool was_clean, u16 code, const String& reason)
+        : Event(event_name)
+        , m_was_clean(was_clean)
+        , m_code(code)
+        , m_reason(reason)
+    {
+    }
+
+    bool m_was_clean { false };
+    u16 m_code { 0 };
+    String m_reason;
+};
+
+}