HTML: BrowsingContext: Remove m_parent and fix is_ancestor_of

`BrowsingContext::m_parent` has been removed from the spec,
and previously `m_parent` was always null.

`BrowsingContext::is_top_level` was already always returning
true before because of that, and the updated spec algorithm
causes assertions to fail.

This fixes the following example:
```html
<a href="about:blank" target="test">a
<iframe name="test">
```
clicking the link twice no longer causes it to open in a new tab.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -3672,7 +3672,9 @@ void Document::make_active()
         m_visibility_state = navigable()->traversable_navigable()->system_visibility_state();
     }
 
-    // 4. Set window's relevant settings object's execution ready flag.
+    // TODO: 4. Queue a new VisibilityStateEntry whose visibility state is document's visibility state and whose timestamp is zero.
+
+    // 5. Set window's relevant settings object's execution ready flag.
     HTML::relevant_settings_object(window).execution_ready = true;
 
     if (m_needs_to_call_page_did_load) {

Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp

@@ -300,7 +300,6 @@ void BrowsingContext::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_page);
     visitor.visit(m_window_proxy);
     visitor.visit(m_group);
-    visitor.visit(m_parent);
     visitor.visit(m_first_child);
     visitor.visit(m_last_child);
     visitor.visit(m_next_sibling);
@@ -321,8 +320,10 @@ JS::NonnullGCPtr<HTML::TraversableNavigable> BrowsingContext::top_level_traversa
 // https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context
 bool BrowsingContext::is_top_level() const
 {
-    // A browsing context that has no parent browsing context is the top-level browsing context for itself and all of the browsing contexts for which it is an ancestor browsing context.
-    return !parent();
+    // FIXME: Remove this. The active document's navigable is sometimes null when it shouldn't be, failing assertions.
+    return true;
+    // A top-level browsing context is a browsing context whose active document's node navigable is a traversable navigable.
+    return active_document() != nullptr && active_document()->navigable() != nullptr && active_document()->navigable()->is_traversable();
 }
 
 JS::GCPtr<BrowsingContext> BrowsingContext::top_level_browsing_context() const
@@ -434,12 +435,28 @@ JS::GCPtr<BrowsingContext> BrowsingContext::next_sibling() const
     return m_next_sibling;
 }
 
-bool BrowsingContext::is_ancestor_of(BrowsingContext const& other) const
+// https://html.spec.whatwg.org/multipage/document-sequences.html#ancestor-browsing-context
+bool BrowsingContext::is_ancestor_of(BrowsingContext const& potential_descendant) const
 {
-    for (auto ancestor = other.parent(); ancestor; ancestor = ancestor->parent()) {
-        if (ancestor == this)
+    // A browsing context potentialDescendant is said to be an ancestor of a browsing context potentialAncestor if the following algorithm returns true:
+
+    // 1. Let potentialDescendantDocument be potentialDescendant's active document.
+    auto const* potential_descendant_document = potential_descendant.active_document();
+
+    // 2. If potentialDescendantDocument is not fully active, then return false.
+    if (!potential_descendant_document->is_fully_active())
+        return false;
+
+    // 3. Let ancestorBCs be the list obtained by taking the browsing context of the active document of each member of potentialDescendantDocument's ancestor navigables.
+    for (auto const& ancestor : potential_descendant_document->ancestor_navigables()) {
+        auto ancestor_browsing_context = ancestor->active_browsing_context();
+
+        // 4. If ancestorBCs contains potentialAncestor, then return true.
+        if (ancestor_browsing_context == this)
             return true;
     }
+
+    // 5. Return false.
     return false;
 }
 
@@ -464,7 +481,12 @@ bool BrowsingContext::is_familiar_with(BrowsingContext const& other) const
 
     // 4. If there exists an ancestor browsing context of B whose active document has the same origin as the active document of A, then return true.
     // NOTE: This includes the case where A is an ancestor browsing context of B.
-    for (auto ancestor = B.parent(); ancestor; ancestor = ancestor->parent()) {
+
+    // If B's active document is not fully active then it cannot have ancestor browsing context
+    if (!B.active_document()->is_fully_active())
+        return false;
+
+    for (auto const& ancestor : B.active_document()->ancestor_navigables()) {
         if (ancestor->active_document()->origin().is_same_origin(A.active_document()->origin()))
             return true;
     }

Userland/Libraries/LibWeb/HTML/BrowsingContext.h

@@ -45,7 +45,6 @@ public:
 
     JS::NonnullGCPtr<HTML::TraversableNavigable> top_level_traversable() const;
 
-    JS::GCPtr<BrowsingContext> parent() const { return m_parent; }
     JS::GCPtr<BrowsingContext> first_child() const;
     JS::GCPtr<BrowsingContext> next_sibling() const;
 
@@ -112,6 +111,8 @@ public:
     Page& page() { return m_page; }
     Page const& page() const { return m_page; }
 
+    u64 virtual_browsing_context_group_id() const { return m_virtual_browsing_context_group_id; }
+
     JS::GCPtr<BrowsingContext> top_level_browsing_context() const;
 
     BrowsingContextGroup* group();
@@ -161,7 +162,6 @@ private:
     // https://html.spec.whatwg.org/multipage/browsers.html#tlbc-group
     JS::GCPtr<BrowsingContextGroup> m_group;
 
-    JS::GCPtr<BrowsingContext> m_parent;
     JS::GCPtr<BrowsingContext> m_first_child;
     JS::GCPtr<BrowsingContext> m_last_child;
     JS::GCPtr<BrowsingContext> m_next_sibling;

Userland/Libraries/LibWeb/MixedContent/AbstractOperations.cpp

@@ -80,7 +80,8 @@ Fetch::Infrastructure::RequestOrResponseBlocking should_fetching_request_be_bloc
         || false
 
         // 4. request’s destination is "document", and request’s target browsing context has no parent browsing context.
-        || (request.destination() == Fetch::Infrastructure::Request::Destination::Document && !(request.client()->target_browsing_context && request.client()->target_browsing_context->parent()))) {
+        // TODO: "parent browsing context" doesn't exist anymore and is a spec bug, seems like it should be `is_top_level`
+        || (request.destination() == Fetch::Infrastructure::Request::Destination::Document && request.client()->target_browsing_context && request.client()->target_browsing_context->is_top_level())) {
         return Fetch::Infrastructure::RequestOrResponseBlocking::Allowed;
     }
 
@@ -104,7 +105,8 @@ Web::Fetch::Infrastructure::RequestOrResponseBlocking should_response_to_request
         || false
 
         // 4. request’s destination is "document", and request’s target browsing context has no parent browsing context.
-        || (request.destination() == Fetch::Infrastructure::Request::Destination::Document && !(request.client()->target_browsing_context && request.client()->target_browsing_context->parent()))) {
+        // TODO: "parent browsing context" doesn't exist anymore and is a spec bug, seems like it should be `is_top_level`
+        || (request.destination() == Fetch::Infrastructure::Request::Destination::Document && request.client()->target_browsing_context && request.client()->target_browsing_context->is_top_level())) {
         return Fetch::Infrastructure::RequestOrResponseBlocking::Allowed;
     }