StyleResolver should update RuleSets lazily.

Source/core/css/StyleRule.h

Index: Source/core/css/StyleRule.h
diff --git a/Source/core/css/StyleRule.h b/Source/core/css/StyleRule.h
index aa319ed734416358497681eebc5c1765e301f7cd..5a0bf89f765427ad6540bd053238877ca2aa5295 100644
--- a/Source/core/css/StyleRule.h
+++ b/Source/core/css/StyleRule.h
@@ -156,6 +156,12 @@ private:
     RefPtr<StylePropertySet> m_properties;
 };
 
+inline const StyleRuleFontFace* toStyleRuleFontFace(const StyleRuleBase* rule)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!rule || rule->isFontFaceRule());
+    return static_cast<const StyleRuleFontFace*>(rule);
+}
+
 class StyleRulePage : public StyleRuleBase {
 public:
     static PassRefPtr<StyleRulePage> create() { return adoptRef(new StyleRulePage); }
@@ -290,6 +296,12 @@ inline const StyleRuleMedia* toStyleRuleMedia(const StyleRuleGroup* rule)
     return static_cast<const StyleRuleMedia*>(rule);
 }
 
+inline const StyleRuleMedia* toStyleRuleMedia(const StyleRuleBase* rule)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!rule || rule->isMediaRule());
+    return static_cast<const StyleRuleMedia*>(rule);
+}
+
 inline const StyleRuleSupports* toStyleRuleSupports(const StyleRuleGroup* rule)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!rule || rule->isSupportsRule());
@@ -302,6 +314,12 @@ inline const StyleRuleRegion* toStyleRuleRegion(const StyleRuleGroup* rule)
     return static_cast<const StyleRuleRegion*>(rule);
 }
 
+inline StyleRuleViewport* toStyleRuleViewport(StyleRuleBase* rule)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!rule || rule->isViewportRule());
+    return static_cast<StyleRuleViewport*>(rule);
+}
+
 class StyleRuleFilter : public StyleRuleBase {
 public:
     static PassRefPtr<StyleRuleFilter> create(const String& filterName) { return adoptRef(new StyleRuleFilter(filterName)); }