Avoid always style recalc when removing stylesheets.

Source/core/css/resolver/ScopedStyleResolver.h

Index: Source/core/css/resolver/ScopedStyleResolver.h
diff --git a/Source/core/css/resolver/ScopedStyleResolver.h b/Source/core/css/resolver/ScopedStyleResolver.h
index 09b1edf48cee02c62852197f1eac396cf8037838..fee466f337bced28bff8908632768069e310df06 100644
--- a/Source/core/css/resolver/ScopedStyleResolver.h
+++ b/Source/core/css/resolver/ScopedStyleResolver.h
@@ -100,6 +100,12 @@ public:
     ScopedStyleTree() : m_scopedResolverForDocument(0), m_buildInDocumentOrder(true) { }
 
     ScopedStyleResolver* ensureScopedStyleResolver(const ContainerNode& scopingNode);
+    ScopedStyleResolver* lookupScopedStyleResolverFor(const ContainerNode* scopingNode)
+    {
+        HashMap<const ContainerNode*, OwnPtr<ScopedStyleResolver> >::iterator it = m_authorStyles.find(scopingNode);
+        return it != m_authorStyles.end() ? it->value.get() : 0;
+    }
+
     ScopedStyleResolver* scopedStyleResolverFor(const ContainerNode& scopingNode);
     ScopedStyleResolver* addScopedStyleResolver(const ContainerNode& scopingNode, bool& isNewEntry);
     void clear();