LibWeb: Introduce the Environment Settings Object

The environment settings object is effectively the context a piece of
script is running under, for example, it contains the origin,
responsible document, realm, global object and event loop for the
current context. This effectively replaces ScriptExecutionContext, but
it cannot be removed in this commit as EventTarget still depends on it.

https://html.spec.whatwg.org/multipage/webappapis.html#environment-settings-object

Userland/Libraries/LibWeb/HTML/Scripting/WindowEnvironmentSettingsObject.cpp

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/WindowObject.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/HTML/Scripting/WindowEnvironmentSettingsObject.h>
+
+namespace Web::HTML {
+
+WindowEnvironmentSettingsObject::WindowEnvironmentSettingsObject(DOM::Window& window, JS::ExecutionContext& execution_context)
+    : EnvironmentSettingsObject(execution_context)
+    , m_window(window)
+{
+}
+
+// https://html.spec.whatwg.org/multipage/window-object.html#set-up-a-window-environment-settings-object
+void WindowEnvironmentSettingsObject::setup(AK::URL& creation_url, JS::ExecutionContext& execution_context)
+{
+    // 1. Let realm be the value of execution context's Realm component.
+    auto* realm = execution_context.realm;
+    VERIFY(realm);
+
+    // 2. Let window be realm's global object.
+    // NOTE: We want to store the Window impl rather than the WindowObject.
+    auto& window = verify_cast<Bindings::WindowObject>(realm->global_object()).impl();
+
+    // 3. Let settings object be a new environment settings object whose algorithms are defined as follows:
+    // NOTE: See the functions defined for this class.
+    auto settings_object = adopt_own(*new WindowEnvironmentSettingsObject(window, execution_context));
+
+    // FIXME: 4. If reservedEnvironment is non-null, then:
+    // FIXME:    1. Set settings object's id to reservedEnvironment's id, target browsing context to reservedEnvironment's target browsing context, and active service worker to reservedEnvironment's active service worker.
+    // FIXME:    2. Set reservedEnvironment's id to the empty string.
+
+    // FIXME: 5. Otherwise, set settings object's id to a new unique opaque string, settings object's target browsing context to null, and settings object's active service worker to null.
+    settings_object->target_browsing_context = nullptr;
+
+    // FIXME: 6. Set settings object's creation URL to creationURL, settings object's top-level creation URL to topLevelCreationURL, and settings object's top-level origin to topLevelOrigin.
+    settings_object->creation_url = creation_url;
+
+    // 7. Set realm's [[HostDefined]] field to settings object.
+    realm->set_host_defined(move(settings_object));
+}
+
+// https://html.spec.whatwg.org/multipage/window-object.html#script-settings-for-window-objects:responsible-document
+RefPtr<DOM::Document> WindowEnvironmentSettingsObject::responsible_document()
+{
+    // Return window's associated Document.
+    return m_window->associated_document();
+}
+
+// https://html.spec.whatwg.org/multipage/window-object.html#script-settings-for-window-objects:api-url-character-encoding
+String WindowEnvironmentSettingsObject::api_url_character_encoding()
+{
+    // Return the current character encoding of window's associated Document.
+    return m_window->associated_document().encoding_or_default();
+}
+
+// https://html.spec.whatwg.org/multipage/window-object.html#script-settings-for-window-objects:api-base-url
+AK::URL WindowEnvironmentSettingsObject::api_base_url()
+{
+    // FIXME: Return the current base URL of window's associated Document.
+    //        (This currently just returns the current document URL, not accounting for <base> elements and such)
+    return m_window->associated_document().url();
+}
+
+// https://html.spec.whatwg.org/multipage/window-object.html#script-settings-for-window-objects:concept-settings-object-origin
+Origin WindowEnvironmentSettingsObject::origin()
+{
+    // Return the origin of window's associated Document.
+    return m_window->associated_document().origin();
+}
+
+// https://html.spec.whatwg.org/multipage/window-object.html#script-settings-for-window-objects:concept-settings-object-cross-origin-isolated-capability
+CanUseCrossOriginIsolatedAPIs WindowEnvironmentSettingsObject::cross_origin_isolated_capability()
+{
+    // FIXME: Return true if both of the following hold, and false otherwise:
+    //          1. realm's agent cluster's cross-origin-isolation mode is "concrete", and
+    //          2. window's associated Document is allowed to use the "cross-origin-isolated" feature.
+    TODO();
+}
+
+}