Avoid always style recalc when removing stylesheets.

Source/core/css/CSSStyleSheet.cpp

Index: Source/core/css/CSSStyleSheet.cpp
diff --git a/Source/core/css/CSSStyleSheet.cpp b/Source/core/css/CSSStyleSheet.cpp
index 05e3b212dc3c2a58cbd54bad508a09cee7a4b1b2..9737560190271c7ebc8e6aa57ef768b288dd7777 100644
--- a/Source/core/css/CSSStyleSheet.cpp
+++ b/Source/core/css/CSSStyleSheet.cpp
@@ -149,15 +149,19 @@ void CSSStyleSheet::didMutateRules()
     ASSERT(m_contents->isMutable());
     ASSERT(m_contents->hasOneClient());
 
-    didMutate();
+    didMutate(PartialRuleUpdate);
 }
 
-void CSSStyleSheet::didMutate()
+void CSSStyleSheet::didMutate(StyleSheetUpdateType updateType)
 {
     Document* owner = ownerDocument();
     if (!owner)
         return;
-    owner->modifiedStyleSheet(this);
+
+    // Need FullStyleUpdate when insertRule or deleteRule,
+    // because StyleSheetCollection::analyzeStyleSheetChange cannot detect partial rule update.
+    StyleResolverUpdateMode updateMode = updateType != PartialRuleUpdate ? AnalyzedStyleUpdate : FullStyleUpdate;
+    owner->modifiedStyleSheet(this, RecalcStyleDeferred, updateMode);
 }
 
 void CSSStyleSheet::reattachChildRuleCSSOMWrappers()