Don't schedule invalidations when attributes changed if not needed or incorrect.

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2783 matching lines @@
         updateId(oldValue, newValue);
     } else if (name == HTMLNames::nameAttr) {
         updateName(oldValue, newValue);
     } else if (name == HTMLNames::forAttr && isHTMLLabelElement(*this)) {
         TreeScope& scope = treeScope();
         if (scope.shouldCacheLabelsByForAttribute())
             updateLabel(scope, oldValue, newValue);
     }
 
     if (oldValue != newValue) {
-        if (inActiveDocument())
+        if (inActiveDocument() && document().styleResolver() && styleChangeType() < SubtreeStyleChange)

[ojan, 2014/05/08 19:14:56]

We chatted about this in person. I'm not sure the styleResolver null-check here
is correct. Re-creating the style resolver does not AFAIK cause a subtree
recalc.

[esprehn, 2014/05/08 19:17:56]

Yeah it doesn't seem like we do that anymore, want to post a patch that removes
all three of them?

             document().ensureStyleResolver().ensureUpdatedRuleFeatureSet().scheduleStyleInvalidationForAttributeChange(name, *this);
 
         if (isUpgradedCustomElement())
             CustomElement::attributeDidChange(this, name.localName(), oldValue, newValue);
     }
 
     if (OwnPtrWillBeRawPtr<MutationObserverInterestGroup> recipients = MutationObserverInterestGroup::createForAttributesMutation(*this, name))
         recipients->enqueueMutationRecord(MutationRecord::createAttributes(this, name, oldValue));
 
     InspectorInstrumentation::willModifyDOMAttr(this, oldValue, newValue);
@@ skipping 483 matching lines @@
 void Element::trace(Visitor* visitor)
 {
     // FIXME: Oilpan: Perform this tracing directly on the element
     // rare data once that is in the heap.
     if (hasRareData())
         elementRareData()->trace(visitor);
     ContainerNode::trace(visitor);
 }
 
 } // namespace WebCore