CSS: Avoid invalidating style when only descendants need updating

Source/core/css/invalidation/InvalidationSet.cpp

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 35 matching lines @@
     if (UNLIKELY(*s_tracingEnabled)) \
         TRACE_STYLE_INVALIDATOR_INVALIDATION_SELECTORPART(element, reason, invalidationSet, singleSelectorPart);
 
 void InvalidationSet::cacheTracingFlag()
 {
     s_tracingEnabled = TRACE_EVENT_API_GET_CATEGORY_ENABLED(TRACE_DISABLED_BY_DEFAULT("devtools.timeline.invalidationTracking"));
 }
 
 InvalidationSet::InvalidationSet()
     : m_allDescendantsMightBeInvalid(false)
+    , m_invalidatesSelf(false)
     , m_customPseudoInvalid(false)
     , m_treeBoundaryCrossing(false)
     , m_insertionPointCrossing(false)
 {
 }
 
 bool InvalidationSet::invalidatesElement(Element& element) const
 {
     if (m_allDescendantsMightBeInvalid)
         return true;
@@ skipping 34 matching lines @@
 {
     // No longer bother combining data structures, since the whole subtree is deemed invalid.
     if (wholeSubtreeInvalid())
         return;
 
     if (other.wholeSubtreeInvalid()) {
         setWholeSubtreeInvalid();
         return;
     }
 
+    if (other.invalidatesSelf())
+        setInvalidatesSelf();
+
     if (other.customPseudoInvalid())
         setCustomPseudoInvalid();
 
     if (other.treeBoundaryCrossing())
         setTreeBoundaryCrossing();
 
     if (other.insertionPointCrossing())
         setInsertionPointCrossing();
 
     if (other.m_classes) {
@@ skipping 149 matching lines @@
 {
     RefPtr<TracedValue> value = TracedValue::create();
     value->beginArray("InvalidationSet");
     toTracedValue(value.get());
     value->endArray();
     fprintf(stderr, "%s\n", value->asTraceFormat().ascii().data());
 }
 #endif // NDEBUG
 
 } // namespace blink