LibWeb: Add hook to HtmlView when a new document is set

Libraries/LibWeb/HtmlView.cpp

@@ -89,6 +89,9 @@ void HtmlView::set_document(Document* new_document)
 
     main_frame().set_document(new_document);
 
+    if (on_set_document)
+        on_set_document(new_document);
+
     if (new_document) {
         new_document->on_layout_updated = [this] {
             layout_and_sync_size();

Libraries/LibWeb/HtmlView.h

@@ -65,6 +65,7 @@ public:
     Function<void(const URL&)> on_load_start;
     Function<void(const Gfx::Bitmap&)> on_favicon_change;
     Function<void(const URL&)> on_url_drop;
+    Function<void(Document*)> on_set_document;
 
     virtual bool accepts_focus() const override { return true; }