StyleResolver should update RuleSets lazily.

Source/core/editing/EditingStyle.cpp

 /*
  * Copyright (C) 2007, 2008, 2009 Apple Computer, Inc.
  * Copyright (C) 2010, 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 1115 matching lines @@
         }
 
         if (mode == OverrideValues || (mode == DoNotOverrideValues && !value))
             m_mutableStyle->setProperty(property.id(), property.value()->cssText(), property.isImportant());
     }
 }
 
 static PassRefPtr<MutableStylePropertySet> styleFromMatchedRulesForElement(Element* element, unsigned rulesToInclude)
 {
     RefPtr<MutableStylePropertySet> style = MutableStylePropertySet::create();
-    RefPtr<StyleRuleList> matchedRules = element->document().styleResolver()->styleRulesForElement(element, rulesToInclude);
+    StyleResolver* styleResolver = element->document().styleResolver();
+    appendPendingStyleSheetsIfNeeded(styleResolver);
+    RefPtr<StyleRuleList> matchedRules = styleResolver->styleRulesForElement(element, rulesToInclude);
     if (matchedRules) {
         for (unsigned i = 0; i < matchedRules->m_list.size(); ++i)
             style->mergeAndOverrideOnConflict(matchedRules->m_list[i]->properties());
     }
     return style.release();
 }
 
 void EditingStyle::mergeStyleFromRules(Element* element)
 {
     RefPtr<MutableStylePropertySet> styleFromMatchedRules = styleFromMatchedRulesForElement(element,
@@ skipping 503 matching lines @@
 {
     for (Node* ancestor = node; ancestor; ancestor = ancestor->parentNode()) {
         RefPtr<CSSComputedStyleDeclaration> ancestorStyle = CSSComputedStyleDeclaration::create(ancestor);
         if (!hasTransparentBackgroundColor(ancestorStyle.get()))
             return ancestorStyle->getPropertyCSSValue(CSSPropertyBackgroundColor);
     }
     return 0;
 }
 
 }