Make RenderObject::style() return a const object

Source/core/css/resolver/StyleResolverState.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 27 matching lines @@
 
 namespace blink {
 
 class CSSAnimationUpdate;
 class FontDescription;
 
 class StyleResolverState {
     STACK_ALLOCATED();
     WTF_MAKE_NONCOPYABLE(StyleResolverState);
 public:
-    StyleResolverState(Document&, const ElementResolveContext&, RenderStyle* parentStyle);
-    StyleResolverState(Document&, Element*, RenderStyle* parentStyle = 0);
+    StyleResolverState(Document&, const ElementResolveContext&, const RenderStyle* parentStyle);
+    StyleResolverState(Document&, Element*, const RenderStyle* parentStyle = 0);
     ~StyleResolverState();
 
     // In FontFaceSet and CanvasRenderingContext2D, we don't have an element to grab the document from.
     // This is why we have to store the document separately.
     Document& document() const { return *m_document; }
     // These are all just pass-through methods to ElementResolveContext.
     Element* element() const { return m_elementContext.element(); }
     const ContainerNode* parentNode() const { return m_elementContext.parentNode(); }
     const RenderStyle* rootElementStyle() const { return m_elementContext.rootElementStyle(); }
     EInsideLink elementLinkState() const { return m_elementContext.elementLinkState(); }
@@ skipping 14 matching lines @@
 
     const CSSToLengthConversionData& cssToLengthConversionData() const { return m_cssToLengthConversionData; }
 
     void setConversionFontSizes(const CSSToLengthConversionData::FontSizes& fontSizes) { m_cssToLengthConversionData.setFontSizes(fontSizes); }
     void setConversionZoom(float zoom) { m_cssToLengthConversionData.setZoom(zoom); }
 
     void setAnimationUpdate(PassOwnPtrWillBeRawPtr<CSSAnimationUpdate>);
     const CSSAnimationUpdate* animationUpdate() { return m_animationUpdate.get(); }
     PassOwnPtrWillBeRawPtr<CSSAnimationUpdate> takeAnimationUpdate();
 
-    void setParentStyle(PassRefPtr<RenderStyle> parentStyle) { m_parentStyle = parentStyle; }
-    const RenderStyle* parentStyle() const { return m_parentStyle.get(); }
-    RenderStyle* parentStyle() { return m_parentStyle.get(); }
+    void setParentStyle(PassRefPtr<RenderStyle> parentStyle) { m_overrideParentStyle = parentStyle; }
+    const RenderStyle* parentStyle() const
+    {
+        if (m_overrideParentStyle)
+            return m_overrideParentStyle.get();
+        return m_parentStyle;
+    }
 
     // FIXME: These are effectively side-channel "out parameters" for the various
     // map functions. When we map from CSS to style objects we use this state object
     // to track various meta-data about that mapping (e.g. if it's cache-able).
     // We need to move this data off of StyleResolverState and closer to the
     // objects it applies to. Possibly separating (immutable) inputs from (mutable) outputs.
     void setApplyPropertyToRegularStyle(bool isApply) { m_applyPropertyToRegularStyle = isApply; }
     void setApplyPropertyToVisitedLinkStyle(bool isApply) { m_applyPropertyToVisitedLinkStyle = isApply; }
     bool applyPropertyToRegularStyle() const { return m_applyPropertyToRegularStyle; }
     bool applyPropertyToVisitedLinkStyle() const { return m_applyPropertyToVisitedLinkStyle; }
@@ skipping 22 matching lines @@
     {
         return m_elementStyleResources.styleImage(document(), document().textLinkColors(), style()->color(), propertyId, value);
     }
 
     FontBuilder& fontBuilder() { return m_fontBuilder; }
     // FIXME: These exist as a primitive way to track mutations to font-related properties
     // on a RenderStyle. As designed, these are very error-prone, as some callers
     // set these directly on the RenderStyle w/o telling us. Presumably we'll
     // want to design a better wrapper around RenderStyle for tracking these mutations
     // and separate it from StyleResolverState.
-    const FontDescription& parentFontDescription() { return m_parentStyle->fontDescription(); }
+    const FontDescription& parentFontDescription() { return parentStyle()->fontDescription(); }
     void setZoom(float f) { m_fontBuilder.didChangeFontParameters(m_style->setZoom(f)); }
     void setEffectiveZoom(float f) { m_fontBuilder.didChangeFontParameters(m_style->setEffectiveZoom(f)); }
     void setWritingMode(WritingMode writingMode) { m_fontBuilder.didChangeFontParameters(m_style->setWritingMode(writingMode)); }
     void setTextOrientation(TextOrientation textOrientation) { m_fontBuilder.didChangeFontParameters(m_style->setTextOrientation(textOrientation)); }
 
 private:
     ElementResolveContext m_elementContext;
     RawPtrWillBeMember<Document> m_document;
 
     // m_style is the primary output for each element's style resolve.
     RefPtr<RenderStyle> m_style;
 
     CSSToLengthConversionData m_cssToLengthConversionData;
 
     // m_parentStyle is not always just ElementResolveContext::parentStyle,
     // so we keep it separate.
-    RefPtr<RenderStyle> m_parentStyle;
+    const RenderStyle* m_parentStyle;
+    RefPtr<RenderStyle> m_overrideParentStyle;
 
     OwnPtrWillBeMember<CSSAnimationUpdate> m_animationUpdate;
 
     bool m_applyPropertyToRegularStyle;
     bool m_applyPropertyToVisitedLinkStyle;
 
     FontBuilder m_fontBuilder;
 
     OwnPtr<CachedUAStyle> m_cachedUAStyle;
 
     ElementStyleResources m_elementStyleResources;
 };
 
 } // namespace blink
 
 #endif // StyleResolverState_h