Avoid unnecessary updateActiveStyle comparing shadow styles.

third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h

Index: third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
diff --git a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
index 2ca625c22f1b4fa36a6ab4a1ef368714d70e3caa..c636ea7a9bf0021d8cc53c22d3a0ec61f252ee56 100644
--- a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
+++ b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.h
@@ -76,6 +76,8 @@ class ScopedStyleResolver final : public GarbageCollected<ScopedStyleResolver> {
   void setNeedsAppendAllSheets() { m_needsAppendAllSheets = true; }
   static void keyframesRulesAdded(const TreeScope&);
   static ContainerNode& invalidationRootForTreeScope(const TreeScope&);
+  CORE_EXPORT static bool haveSameStyles(const ScopedStyleResolver*,

[sashab, 2017/01/04 00:39:33]

I sort of agree with sigbjornf that this could be a bool operator==, but it
sounds like you're not actually comparing equality, just that the two styles are
equal in the same order. Also either could be null.

+                                         const ScopedStyleResolver*);
 
   DECLARE_TRACE();