LibWeb: Change update_style() to update animated style only if needed

Instead of invalidating animated style properties whenever
`Document::update_style()` is called, now we only do that when
animations might have actually progressed. We still have to ensure
animated properties are up-to-date in `update_style()` to ensure that
JS methods can access updated style properties.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -1151,17 +1151,7 @@ void Document::update_style()
     if (!browsing_context())
         return;
 
-    for (auto& timeline : m_associated_animation_timelines) {
-        for (auto& animation : timeline->associated_animations()) {
-            if (auto effect = animation->effect(); effect && effect->target())
-                effect->target()->reset_animated_css_properties();
-        }
-
-        for (auto& animation : timeline->associated_animations()) {
-            if (auto effect = animation->effect())
-                effect->update_style_properties();
-        }
-    }
+    update_animated_style_if_needed();
 
     if (!needs_full_style_update() && !needs_style_update() && !child_needs_style_update())
         return;
@@ -1187,6 +1177,25 @@ void Document::update_style()
     m_needs_full_style_update = false;
 }
 
+void Document::update_animated_style_if_needed()
+{
+    if (!m_needs_animated_style_update)
+        return;
+
+    for (auto& timeline : m_associated_animation_timelines) {
+        for (auto& animation : timeline->associated_animations()) {
+            if (auto effect = animation->effect(); effect && effect->target())
+                effect->target()->reset_animated_css_properties();
+        }
+
+        for (auto& animation : timeline->associated_animations()) {
+            if (auto effect = animation->effect())
+                effect->update_style_properties();
+        }
+    }
+    m_needs_animated_style_update = false;
+}
+
 void Document::update_paint_and_hit_testing_properties_if_needed()
 {
     if (!m_needs_to_resolve_paint_only_properties)
@@ -4055,6 +4064,8 @@ void Document::ensure_animation_timer()
                 for (auto& animation : timeline->associated_animations())
                     dispatch_events_for_animation_if_necessary(animation);
             }
+
+            m_needs_animated_style_update = true;
         }));
     }
 

Userland/Libraries/LibWeb/DOM/Document.h

@@ -211,6 +211,7 @@ public:
     void update_style();
     void update_layout();
     void update_paint_and_hit_testing_properties_if_needed();
+    void update_animated_style_if_needed();
 
     void set_needs_layout();
 
@@ -736,6 +737,8 @@ private:
 
     bool m_needs_full_style_update { false };
 
+    bool m_needs_animated_style_update { false };
+
     HashTable<JS::GCPtr<NodeIterator>> m_node_iterators;
 
     HashTable<JS::NonnullGCPtr<DocumentObserver>> m_document_observers;