Avoid style invalidation for empty sets.

Source/core/css/invalidation/DescendantInvalidationSet.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 181 matching lines @@
         return;
     ensureAttributeSet().add(attribute);
 }
 
 void DescendantInvalidationSet::setWholeSubtreeInvalid()
 {
     if (m_allDescendantsMightBeInvalid)
         return;
 
     m_allDescendantsMightBeInvalid = true;
+    m_customPseudoInvalid = false;
     m_treeBoundaryCrossing = false;
     m_insertionPointCrossing = false;
     m_classes = nullptr;
     m_ids = nullptr;
     m_tagNames = nullptr;
     m_attributes = nullptr;
 }
 
 void DescendantInvalidationSet::trace(Visitor* visitor)
 {
@@ skipping 56 matching lines @@
 {
     RefPtr<TracedValue> value = TracedValue::create();
     value->beginArray("DescendantInvalidationSet");
     toTracedValue(value.get());
     value->endArray();
     fprintf(stderr, "%s\n", value->asTraceFormat().ascii().data());
 }
 #endif // NDEBUG
 
 } // namespace blink