LibWeb: Implement "browsing context group" concept from the HTML spec

Userland/Libraries/LibWeb/HTML/BrowsingContextGroup.cpp

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/HTML/BrowsingContext.h>
+#include <LibWeb/HTML/BrowsingContextGroup.h>
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/browsers.html#browsing-context-group-set
+static HashTable<BrowsingContextGroup*>& user_agent_browsing_context_group_set()
+{
+    static HashTable<BrowsingContextGroup*> set;
+    return set;
+}
+
+BrowsingContextGroup::BrowsingContextGroup(Web::Page& page)
+    : m_page(page)
+{
+    user_agent_browsing_context_group_set().set(this);
+}
+
+BrowsingContextGroup::~BrowsingContextGroup()
+{
+    user_agent_browsing_context_group_set().remove(this);
+}
+
+// https://html.spec.whatwg.org/multipage/browsers.html#creating-a-new-browsing-context-group
+NonnullRefPtr<BrowsingContextGroup> BrowsingContextGroup::create_a_new_browsing_context_group(Web::Page& page)
+{
+    // 1. Let group be a new browsing context group.
+    // 2. Append group to the user agent's browsing context group set.
+    auto group = adopt_ref(*new BrowsingContextGroup(page));
+
+    // 3. Let browsingContext be the result of creating a new browsing context with null, null, and group.
+    auto browsing_context = BrowsingContext::create_a_new_browsing_context(page, nullptr, nullptr, group);
+
+    // 4. Append browsingContext to group.
+    group->append(move(browsing_context));
+
+    // 5. Return group.
+    return group;
+}
+
+// https://html.spec.whatwg.org/multipage/browsers.html#bcg-append
+void BrowsingContextGroup::append(BrowsingContext& browsing_context)
+{
+    VERIFY(browsing_context.is_top_level());
+
+    // 1. Append browsingContext to group's browsing context set.
+    m_browsing_context_set.set(browsing_context);
+
+    // 2. Set browsingContext's group to group.
+    browsing_context.set_group(this);
+}
+
+}