Make RenderObject::style() return a const object

Source/core/css/resolver/StyleResolver.h

Index: Source/core/css/resolver/StyleResolver.h
diff --git a/Source/core/css/resolver/StyleResolver.h b/Source/core/css/resolver/StyleResolver.h
index edec7dc76e4ab20731bc5cde30fae28635ee0b80..ed8b02ef726b484179952c4c2962f04ef14b1037 100644
--- a/Source/core/css/resolver/StyleResolver.h
+++ b/Source/core/css/resolver/StyleResolver.h
@@ -105,14 +105,14 @@ public:
     void pushParentElement(Element&);
     void popParentElement(Element&);
 
-    PassRefPtr<LayoutStyle> styleForElement(Element*, LayoutStyle* parentStyle = 0, StyleSharingBehavior = AllowStyleSharing,
+    PassRefPtr<LayoutStyle> styleForElement(Element*, const LayoutStyle* parentStyle = 0, StyleSharingBehavior = AllowStyleSharing,
         RuleMatchingBehavior = MatchAllRules);
 
-    PassRefPtr<LayoutStyle> styleForKeyframe(Element&, const LayoutStyle&, LayoutStyle* parentStyle, const StyleRuleKeyframe*, const AtomicString& animationName);
+    PassRefPtr<LayoutStyle> styleForKeyframe(Element&, const LayoutStyle&, const LayoutStyle* parentStyle, const StyleRuleKeyframe*, const AtomicString& animationName);
     static PassRefPtrWillBeRawPtr<AnimatableValue> createAnimatableValueSnapshot(Element&, CSSPropertyID, CSSValue&);
     static PassRefPtrWillBeRawPtr<AnimatableValue> createAnimatableValueSnapshot(StyleResolverState&, CSSPropertyID, CSSValue&);
 
-    PassRefPtr<LayoutStyle> pseudoStyleForElement(Element*, const PseudoStyleRequest&, LayoutStyle* parentStyle);
+    PassRefPtr<LayoutStyle> pseudoStyleForElement(Element*, const PseudoStyleRequest&, const LayoutStyle* parentStyle);
 
     PassRefPtr<LayoutStyle> styleForPage(int pageIndex);
     PassRefPtr<LayoutStyle> defaultStyleForElement();
@@ -247,7 +247,7 @@ private:
     bool isFirstPage(int pageIndex) const;
     String pageName(int pageIndex) const;
 
-    bool pseudoStyleForElementInternal(Element&, const PseudoStyleRequest&, LayoutStyle* parentStyle, StyleResolverState&);
+    bool pseudoStyleForElementInternal(Element&, const PseudoStyleRequest&, const LayoutStyle* parentStyle, StyleResolverState&);
 
     PassRefPtrWillBeRawPtr<PseudoElement> createPseudoElement(Element* parent, PseudoId);