LibWeb: Add a document observer to be notified upon becoming active

Libraries/LibWeb/DOM/Document.cpp

@@ -3887,6 +3887,10 @@ void Document::make_active()
         navigable()->traversable_navigable()->page().client().page_did_finish_loading(url());
         m_needs_to_call_page_did_load = false;
     }
+
+    notify_each_document_observer([&](auto const& document_observer) {
+        return document_observer.document_became_active();
+    });
 }
 
 HTML::ListOfAvailableImages& Document::list_of_available_images()

Libraries/LibWeb/DOM/DocumentObserver.cpp

@@ -23,6 +23,7 @@ void DocumentObserver::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
     visitor.visit(m_document);
+    visitor.visit(m_document_became_active);
     visitor.visit(m_document_became_inactive);
     visitor.visit(m_document_completely_loaded);
     visitor.visit(m_document_readiness_observer);
@@ -36,6 +37,14 @@ void DocumentObserver::finalize()
     m_document->unregister_document_observer({}, *this);
 }
 
+void DocumentObserver::set_document_became_active(Function<void()> callback)
+{
+    if (callback)
+        m_document_became_active = GC::create_function(vm().heap(), move(callback));
+    else
+        m_document_became_active = nullptr;
+}
+
 void DocumentObserver::set_document_became_inactive(Function<void()> callback)
 {
     if (callback)

Libraries/LibWeb/DOM/DocumentObserver.h

@@ -20,6 +20,9 @@ class DocumentObserver final : public Bindings::PlatformObject {
     GC_DECLARE_ALLOCATOR(DocumentObserver);
 
 public:
+    [[nodiscard]] GC::Ptr<GC::Function<void()>> document_became_active() const { return m_document_became_active; }
+    void set_document_became_active(Function<void()>);
+
     [[nodiscard]] GC::Ptr<GC::Function<void()>> document_became_inactive() const { return m_document_became_inactive; }
     void set_document_became_inactive(Function<void()>);
 
@@ -42,6 +45,7 @@ private:
     virtual void finalize() override;
 
     GC::Ref<DOM::Document> m_document;
+    GC::Ptr<GC::Function<void()>> m_document_became_active;
     GC::Ptr<GC::Function<void()>> m_document_became_inactive;
     GC::Ptr<GC::Function<void()>> m_document_completely_loaded;
     GC::Ptr<GC::Function<void(HTML::DocumentReadyState)>> m_document_readiness_observer;