LibWeb: Schedule repainting from EventLoop::process()

In this change, updating layout and painting are moved to the EventLoop
processing steps. This modification allows the addition of resize
observation dispatching that needs to happen in event loop processing
steps and must occur in the following order relative to layout and
painting:

1. Update layout.
2. Gather and broadcast resize observations.
3. Paint.

Userland/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp

@@ -15,6 +15,7 @@
 #include <LibWeb/HTML/Window.h>
 #include <LibWeb/HighResolutionTime/Performance.h>
 #include <LibWeb/HighResolutionTime/TimeOrigin.h>
+#include <LibWeb/Page/Page.h>
 #include <LibWeb/Platform/EventLoopPlugin.h>
 #include <LibWeb/Platform/Timer.h>
 
@@ -213,7 +214,12 @@ void EventLoop::process()
 
     // FIXME:     15. Invoke the mark paint timing algorithm for each Document object in docs.
 
-    // FIXME:     16. For each fully active Document in docs, update the rendering or user interface of that Document and its browsing context to reflect the current state.
+    // 16. For each fully active Document in docs, update the rendering or user interface of that Document and its browsing context to reflect the current state.
+    for_each_fully_active_document_in_docs([&](DOM::Document& document) {
+        auto* browsing_context = document.browsing_context();
+        auto& page = browsing_context->page();
+        page.client().schedule_repaint();
+    });
 
     // 13. If all of the following are true
     // - this is a window event loop