Avoid unnecessary updateActiveStyle comparing shadow styles.

third_party/WebKit/Source/core/dom/shadow/ElementShadow.cpp

 /*
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 #include "core/dom/shadow/ElementShadow.h"
 
 #include "core/css/StyleSheetList.h"
+#include "core/css/resolver/ScopedStyleResolver.h"
 #include "core/dom/StyleChangeReason.h"
 #include "core/dom/shadow/ElementShadowV0.h"
 #include "core/frame/Deprecation.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "platform/EventDispatchForbiddenScope.h"
 #include "platform/ScriptForbiddenScope.h"
 
 namespace blink {
 
 ElementShadow* ElementShadow::create() {
@@ skipping 92 matching lines @@
     v0().clearDistribution();
 }
 
 bool ElementShadow::hasSameStyles(const ElementShadow& other) const {
   ShadowRoot* root = &youngestShadowRoot();
   ShadowRoot* otherRoot = &other.youngestShadowRoot();
   while (root || otherRoot) {
     if (!root || !otherRoot)
       return false;
 
-    StyleSheetList& list = root->styleSheets();
-    StyleSheetList& otherList = otherRoot->styleSheets();
+    if (!ScopedStyleResolver::haveSameStyles(
+            root->scopedStyleResolver(), otherRoot->scopedStyleResolver())) {
+      return false;
+    }
 
-    if (list.length() != otherList.length())
-      return false;
-
-    for (size_t i = 0; i < list.length(); i++) {
-      if (toCSSStyleSheet(list.item(i))->contents() !=
-          toCSSStyleSheet(otherList.item(i))->contents())
-        return false;
-    }
     root = root->olderShadowRoot();
     otherRoot = otherRoot->olderShadowRoot();
   }
 
   return true;
 }
 
 void ElementShadow::distribute() {
   if (isV1())
     youngestShadowRoot().distributeV1();
   else
     v0().distribute();
 }
 
 DEFINE_TRACE(ElementShadow) {
   visitor->trace(m_elementShadowV0);
   visitor->trace(m_shadowRoot);
 }
 
 DEFINE_TRACE_WRAPPERS(ElementShadow) {
   visitor->traceWrappers(m_elementShadowV0);
   visitor->traceWrappers(m_shadowRoot);
 }
 
 }  // namespace blink