StyleResolver should update RuleSets lazily.

Source/core/dom/ShadowTreeStyleSheetCollection.cpp

Index: Source/core/dom/ShadowTreeStyleSheetCollection.cpp
diff --git a/Source/core/dom/ShadowTreeStyleSheetCollection.cpp b/Source/core/dom/ShadowTreeStyleSheetCollection.cpp
index f77ff81e064f0ef3aa587d6021185e834b1cecb4..908119a36aa3d729be613fc066c31933bca5f0ca 100644
--- a/Source/core/dom/ShadowTreeStyleSheetCollection.cpp
+++ b/Source/core/dom/ShadowTreeStyleSheetCollection.cpp
@@ -113,10 +113,11 @@ bool ShadowTreeStyleSheetCollection::updateActiveStyleSheets(StyleEngine* collec
             // We should not destroy StyleResolver when we find any stylesheet update in a shadow tree.
             // In this case, we will reset rulesets created from style elements in the shadow tree.
             resetAllRuleSetsInTreeScope(styleResolver);
-            styleResolver->appendAuthorStyleSheets(0, activeCSSStyleSheets);
+            styleResolver->removePendingAuthorStyleSheets(m_activeAuthorStyleSheets);
+            styleResolver->lazyAppendAuthorStyleSheets(0, activeCSSStyleSheets);
         } else {
             ASSERT(styleResolverUpdateType == Additive);
-            styleResolver->appendAuthorStyleSheets(m_activeAuthorStyleSheets.size(), activeCSSStyleSheets);
+            styleResolver->lazyAppendAuthorStyleSheets(m_activeAuthorStyleSheets.size(), activeCSSStyleSheets);
         }
     }
     if (requiresFullStyleRecalc)