LibWeb: Implement ErrorEvent

This will be used by the new EventTarget to check if it needs to do
special error event handling. Currently it isn't used for anything
else.

Userland/Libraries/LibWeb/HTML/ErrorEvent.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/DOM/Event.h>
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/webappapis.html#erroreventinit
+struct ErrorEventInit : public DOM::EventInit {
+    String message { "" };
+    String filename { "" }; // FIXME: This should be a USVString.
+    u32 lineno { 0 };
+    u32 colno { 0 };
+    JS::Value error { JS::js_null() };
+};
+
+// https://html.spec.whatwg.org/multipage/webappapis.html#errorevent
+class ErrorEvent final : public DOM::Event {
+public:
+    using WrapperType = Bindings::ErrorEventWrapper;
+
+    static NonnullRefPtr<ErrorEvent> create(FlyString const& event_name, ErrorEventInit const& event_init = {})
+    {
+        return adopt_ref(*new ErrorEvent(event_name, event_init));
+    }
+
+    static NonnullRefPtr<ErrorEvent> create_with_global_object(Bindings::WindowObject&, FlyString const& event_name, ErrorEventInit const& event_init)
+    {
+        return ErrorEvent::create(event_name, event_init);
+    }
+
+    virtual ~ErrorEvent() override = default;
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-message
+    String const& message() const { return m_message; }
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-filename
+    String const& filename() const { return m_filename; }
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-lineno
+    u32 lineno() const { return m_lineno; }
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-colno
+    u32 colno() const { return m_colno; }
+
+    // https://html.spec.whatwg.org/multipage/webappapis.html#dom-errorevent-error
+    JS::Value error() const { return m_error.value(); }
+
+private:
+    ErrorEvent(FlyString const& event_name, ErrorEventInit const& event_init)
+        : DOM::Event(event_name)
+        , m_message(event_init.message)
+        , m_filename(event_init.filename)
+        , m_lineno(event_init.lineno)
+        , m_colno(event_init.colno)
+        , m_error(JS::make_handle(event_init.error))
+    {
+    }
+
+    String m_message { "" };
+    String m_filename { "" }; // FIXME: This should be a USVString.
+    u32 m_lineno { 0 };
+    u32 m_colno { 0 };
+    JS::Handle<JS::Value> m_error;
+};
+
+}