Make RenderObject::style() return a const object

Source/core/layout/style/LayoutStyle.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * 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
@@ skipping 240 matching lines @@
         mutable unsigned hasViewportUnits : 1;
 
         // 32 bits
 
         unsigned pageBreakBefore : 2; // EPageBreak
         unsigned pageBreakAfter : 2; // EPageBreak
         unsigned pageBreakInside : 2; // EPageBreak
 
         unsigned styleType : 6; // PseudoId
         unsigned pseudoBits : 8;
-        unsigned explicitInheritance : 1; // Explicitly inherits a non-inherited property
-        unsigned unique : 1; // Style can not be shared.
+        // FIXME: |explicitInheritance| should be moved to ElementRareData.
+        mutable unsigned explicitInheritance : 1; // Explicitly inherits a non-inherited property
+        mutable unsigned unique : 1; // Style can not be shared.
 
         unsigned emptyState : 1;
 
         unsigned affectedByFocus : 1;
         unsigned affectedByHover : 1;
         unsigned affectedByActive : 1;
         unsigned affectedByDrag : 1;
 
         unsigned isLink : 1;
         // If you add more style bits here, you will also need to update LayoutStyle::copyNonInheritedFrom()
@@ skipping 486 matching lines @@
     bool isGridAutoFlowAlgorithmSparse() const { return (rareNonInheritedData->m_grid->m_gridAutoFlow & InternalAutoFlowAlgorithmSparse) == InternalAutoFlowAlgorithmSparse; }
     bool isGridAutoFlowAlgorithmDense() const { return (rareNonInheritedData->m_grid->m_gridAutoFlow & InternalAutoFlowAlgorithmDense) == InternalAutoFlowAlgorithmDense; }
     const GridTrackSize& gridAutoColumns() const { return rareNonInheritedData->m_grid->m_gridAutoColumns; }
     const GridTrackSize& gridAutoRows() const { return rareNonInheritedData->m_grid->m_gridAutoRows; }
 
     const GridPosition& gridColumnStart() const { return rareNonInheritedData->m_gridItem->m_gridColumnStart; }
     const GridPosition& gridColumnEnd() const { return rareNonInheritedData->m_gridItem->m_gridColumnEnd; }
     const GridPosition& gridRowStart() const { return rareNonInheritedData->m_gridItem->m_gridRowStart; }
     const GridPosition& gridRowEnd() const { return rareNonInheritedData->m_gridItem->m_gridRowEnd; }
 
     ShadowList* boxShadow() const { return rareNonInheritedData->m_boxShadow.get(); }

[pdr., 2015/02/18 22:30:57]

Returning non-const pointers from const objects can introduce tricky bugs. Do we
plan on constifying or removing these? (here, and elsewhere in this class)

 
     EBoxDecorationBreak boxDecorationBreak() const { return m_box->boxDecorationBreak(); }
     StyleReflection* boxReflect() const { return rareNonInheritedData->m_boxReflect.get(); }
     bool reflectionDataEquivalent(const LayoutStyle* otherStyle) const { return rareNonInheritedData->reflectionDataEquivalent(*otherStyle->rareNonInheritedData); }
 
     // FIXME: reflections should belong to this helper function but they are currently handled
     // through their self-painting layers. So the rendering code doesn't account for them.
     bool hasVisualOverflowingEffect() const { return boxShadow() || hasBorderImageOutsets() || hasOutline(); }
 
     EBoxSizing boxSizing() const { return m_box->boxSizing(); }
@@ skipping 670 matching lines @@
     {
         if (v == writingMode())
             return false;
 
         inherited_flags.m_writingMode = v;
         return true;
     }
 
     // A unique style is one that has matches something that makes it impossible to share.
     bool unique() const { return noninherited_flags.unique; }
-    void setUnique() { noninherited_flags.unique = true; }
+    void setUnique() const { noninherited_flags.unique = true; }
 
     bool isSharable() const;
 
     bool emptyState() const { return noninherited_flags.emptyState; }
     void setEmptyState(bool b) { setUnique(); noninherited_flags.emptyState = b; }
 
     Color visitedDependentColor(int colorProperty) const;
 
-    void setHasExplicitlyInheritedProperties() { noninherited_flags.explicitInheritance = true; }
+    void setHasExplicitlyInheritedProperties() const { noninherited_flags.explicitInheritance = true; }
     bool hasExplicitlyInheritedProperties() const { return noninherited_flags.explicitInheritance; }
 
     bool hasBoxDecorations() const { return hasBorder() || hasBorderRadius() || hasOutline() || hasAppearance() || boxShadow() || hasFilter() || resize() != RESIZE_NONE; }
 
     bool borderObscuresBackground() const;
     void getBorderEdgeInfo(BorderEdge edges[], bool includeLogicalLeftEdge = true, bool includeLogicalRightEdge = true) const;
 
     // Initial values for all the properties
     static EBorderCollapse initialBorderCollapse() { return BSEPARATE; }
     static EBorderStyle initialBorderStyle() { return BNONE; }
@@ skipping 371 matching lines @@
 }
 
 inline bool LayoutStyle::hasPseudoElementStyle() const
 {
     return noninherited_flags.pseudoBits & PSEUDO_ELEMENT_MASK;
 }
 
 } // namespace blink
 
 #endif // LayoutStyle_h