Avoid unnecessary updateActiveStyle comparing shadow styles.

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

Index: third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
index b4e489dc1471e02136c322e3a566e99535d8a68a..074ac0d18b9c79829035afcd08414b958d35a1d0 100644
--- a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
@@ -298,6 +298,20 @@ void ScopedStyleResolver::addTreeBoundaryCrossingRules(
       RuleSubSet::create(parentStyleSheet, sheetIndex, ruleSetForScope));
 }
 
+bool ScopedStyleResolver::hasSameStyles(const ScopedStyleResolver* first,
+                                        const ScopedStyleResolver* second) {
+  unsigned firstCount = first ? first->m_authorStyleSheets.size() : 0;
+  unsigned secondCount = second ? second->m_authorStyleSheets.size() : 0;

[sof, 2017/01/03 18:48:34]

Using size_t would avoid the (unlikely) problem of the two size_t conversions
end up with the same unsigned values, despite being different sizes. And prevent
some compilers from issuing warnings.

[rune, 2017/01/03 21:33:01]

Done.

+  if (firstCount != secondCount)
+    return false;
+  while (firstCount--) {
+    if (first->m_authorStyleSheets[firstCount]->contents() !=
+        second->m_authorStyleSheets[firstCount]->contents())
+      return false;
+  }
+  return true;
+}
+
 DEFINE_TRACE(ScopedStyleResolver::RuleSubSet) {
   visitor->trace(m_parentStyleSheet);
   visitor->trace(m_ruleSet);