Don't force recalc if there are no shadow boundary crossing rules

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 1603 matching lines @@
 
     // If "rem" units are used anywhere in the document, and if the document element's font size changes, then go ahead and force font updating
     // all the way down the tree. This is simpler than having to maintain a cache of objects (and such font size changes should be rare anyway).
     if (document().styleEngine()->usesRemUnits() && document().documentElement() == this && oldStyle->fontSize() != newStyle->fontSize()) {
         // Cached RenderStyles may depend on the re units.
         document().ensureStyleResolver().invalidateMatchedPropertiesCache();
         return Force;
     }
 
     if (styleChangeType() >= SubtreeStyleChange)
-        return Force;
+        return document().ensureStyleResolver().treeBoundaryCrossingRules().isEmpty() ? Inherit : Force;

[esprehn, 2013/12/20 19:11:43]

I'm not sure if this will work with adding <style> elements to ShadowRoots since
sorvell said that a <style> in one ShadowRoot should apply to all ShadowRoots.
Does that work yet? We might need to do setNeedsStyleRecalc on each ShadowRoot
in that case.

It might be nice to add a method in StyleResolver.h like
hasTreeBoundaryCrossingRules() const { return ... } to hide the isEmpty() check
since we might not expose that API. We can do that in the future if you don't
want to mess with it in this patch.

 
     return max(localChange, change);
 }
 
 void Element::recalcChildStyle(StyleRecalcChange change)
 {
     ASSERT(document().inStyleRecalc());
     ASSERT(change >= Inherit || childNeedsStyleRecalc());
     ASSERT(!needsStyleRecalc());
 
@@ skipping 2014 matching lines @@
     // Before doing so, we need to resolve issues in HTMLSelectElement::recalcListItems
     // and RenderMenuList::setText. See also https://bugs.webkit.org/show_bug.cgi?id=88405
     if (hasTagName(optionTag) || hasTagName(optgroupTag))
         return false;
     if (FullscreenElementStack::isActiveFullScreenElement(this))
         return false;
     return true;
 }
 
 } // namespace WebCore