LibWeb: Skip queuing a rendering task if task queue already contains it

If, by the time we need to schedule rendering of the next frame, the
previous one is still not processed, we could skip it instead of growing
task queue.

Should help with https://github.com/LadybirdBrowser/ladybird/issues/1647

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

@@ -221,6 +221,11 @@ void EventLoop::queue_task_to_update_the_rendering()
     // 2. Set eventLoop's last render opportunity time to the unsafe shared current time.
     m_last_render_opportunity_time = HighResolutionTime::unsafe_shared_current_time();
 
+    // OPTIMIZATION: If there are already rendering tasks in the queue, we don't need to queue another one.
+    if (m_task_queue->has_rendering_tasks()) {
+        return;
+    }
+
     // 3. For each navigable that has a rendering opportunity, queue a global task on the rendering task source given navigable's active window to update the rendering:
     for (auto& navigable : all_navigables()) {
         if (!navigable->is_traversable())

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

@@ -88,4 +88,13 @@ Task const* TaskQueue::last_added_task() const
     return m_tasks.last();
 }
 
+bool TaskQueue::has_rendering_tasks() const
+{
+    for (auto const& task : m_tasks) {
+        if (task->source() == Task::Source::Rendering)
+            return true;
+    }
+    return false;
+}
+
 }

Userland/Libraries/LibWeb/HTML/EventLoop/TaskQueue.h

@@ -23,6 +23,7 @@ public:
     bool is_empty() const { return m_tasks.is_empty(); }
 
     bool has_runnable_tasks() const;
+    bool has_rendering_tasks() const;
 
     void add(JS::NonnullGCPtr<HTML::Task>);
     JS::GCPtr<HTML::Task> take_first_runnable();