LibWeb: Add LocationObject::relevant_document()

https://html.spec.whatwg.org/multipage/history.html#relevant-document

> A Location object has an associated relevant Document, which is this
> Location object's relevant global object's browsing context's active
> document, if this Location object's relevant global object's browsing
> context is non-null, and null otherwise.

Userland/Libraries/LibWeb/Bindings/LocationObject.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <[email protected]>
+ * Copyright (c) 2022, Linus Groh <[email protected]>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -45,6 +46,16 @@ LocationObject::~LocationObject()
 {
 }
 
+// https://html.spec.whatwg.org/multipage/history.html#relevant-document
+DOM::Document const* LocationObject::relevant_document() const
+{
+ // A Location object has an associated relevant Document, which is this Location object's
+ // relevant global object's browsing context's active document, if this Location object's
+ // relevant global object's browsing context is non-null, and null otherwise.
+ auto* browsing_context = static_cast<WindowObject&>(global_object()).impl().browsing_context();
+ return browsing_context ? browsing_context->active_document() : nullptr;
+}
+
 // https://html.spec.whatwg.org/multipage/history.html#dom-location-href
 JS_DEFINE_NATIVE_FUNCTION(LocationObject::href_getter)
 {

Userland/Libraries/LibWeb/Bindings/LocationObject.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Andreas Kling <[email protected]>
+ * Copyright (c) 2022, Linus Groh <[email protected]>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -29,6 +30,8 @@ class LocationObject final : public JS::Object {
  // but we don't have the infrastructure in place to implement them yet.
 
 private:
+ DOM::Document const* relevant_document() const;
+
  JS_DECLARE_NATIVE_FUNCTION(reload);
  JS_DECLARE_NATIVE_FUNCTION(replace);