LibWeb: Add basic skeleton of HTML "session history" to BrowsingContext

Userland/Libraries/LibWeb/HTML/SessionHistoryEntry.h

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+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/URL.h>
+#include <AK/WeakPtr.h>
+#include <LibWeb/Forward.h>
+#include <LibWeb/HTML/PolicyContainers.h>
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/history.html#scroll-restoration-mode
+enum class ScrollRestorationMode {
+    // https://html.spec.whatwg.org/multipage/history.html#dom-scrollrestoration-auto
+    // The user agent is responsible for restoring the scroll position upon navigation.
+    Auto,
+
+    // https://html.spec.whatwg.org/multipage/history.html#dom-scrollrestoration-manual
+    // The page is responsible for restoring the scroll position and the user agent does not attempt to do so automatically.
+    Manual,
+};
+
+// https://html.spec.whatwg.org/multipage/history.html#session-history-entry
+struct SessionHistoryEntry {
+    // URL, a URL
+    AK::URL url;
+
+    // document, a Document or null
+    WeakPtr<DOM::Document> document;
+
+    // serialized state, which is serialized state or null, initially null
+    Optional<String> serialized_state;
+
+    // policy container, a policy container or null
+    Optional<PolicyContainer> policy_container;
+
+    // scroll restoration mode, a scroll restoration mode, initially "auto"
+    ScrollRestorationMode scroll_restoration_mode { ScrollRestorationMode::Auto };
+
+    // FIXME: scroll position data, which is scroll position data for the document's restorable scrollable regions
+
+    // browsing context name, a browsing context name or null, initially null
+    Optional<String> browsing_context_name;
+
+    // FIXME: persisted user state, which is implementation-defined, initially null
+    // NOTE: This is where we could remember the state of form controls, for example.
+};
+
+}