Stop explicit inheritance if LayoutStyle doesn't change.

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 188 matching lines @@
         unsigned _pointerEvents : 4; // EPointerEvents
         unsigned _insideLink : 2; // EInsideLink
 
         // CSS Text Layout Module Level 3: Vertical writing support
         unsigned m_writingMode : 2; // WritingMode
         // 42 bits
     } inherited_flags;
 
 // don't inherit
     struct NonInheritedFlags {
+        // Compare computed styles, differences in other flags should not cause an inequality.
         bool operator==(const NonInheritedFlags& other) const
         {
             return effectiveDisplay == other.effectiveDisplay
                 && originalDisplay == other.originalDisplay
                 && overflowX == other.overflowX
                 && overflowY == other.overflowY
                 && verticalAlign == other.verticalAlign
                 && clear == other.clear
                 && position == other.position
                 && floating == other.floating
                 && tableLayout == other.tableLayout
+                && unicodeBidi == other.unicodeBidi
+                // hasViewportUnits
                 && pageBreakBefore == other.pageBreakBefore
                 && pageBreakAfter == other.pageBreakAfter
-                && pageBreakInside == other.pageBreakInside
-                && styleType == other.styleType
-                && affectedByFocus == other.affectedByFocus
-                && affectedByHover == other.affectedByHover
-                && affectedByActive == other.affectedByActive
-                && affectedByDrag == other.affectedByDrag
-                && pseudoBits == other.pseudoBits
-                && unicodeBidi == other.unicodeBidi
-                && explicitInheritance == other.explicitInheritance
-                && unique == other.unique
-                && emptyState == other.emptyState
-                && isLink == other.isLink;
+                && pageBreakInside == other.pageBreakInside;
+                // styleType
+                // pseudoBits
+                // explicitInheritance
+                // unique
+                // emptyState
+                // affectedByFocus
+                // affectedByHover
+                // affectedByActive
+                // affectedByDrag
+                // isLink
         }
 
         bool operator!=(const NonInheritedFlags& other) const { return !(*this == other); }
 
         unsigned effectiveDisplay : 5; // EDisplay
         unsigned originalDisplay : 5; // EDisplay
         unsigned overflowX : 3; // EOverflow
         unsigned overflowY : 3; // EOverflow
         unsigned verticalAlign : 4; // EVerticalAlign
         unsigned clear : 2; // EClear
@@ skipping 18 matching lines @@
         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()
+        // If you add more style bits here, you will also need to update LayoutStyle::copyNonInheritedFromCached()
         // 62 bits
     } noninherited_flags;
 
 // !END SYNC!
 
 protected:
     void setBitDefaults()
     {
         inherited_flags._empty_cells = initialEmptyCells();
         inherited_flags._caption_side = initialCaptionSide();
@@ skipping 61 matching lines @@
     static ItemPosition resolveJustification(const LayoutStyle& parentStyle, const LayoutStyle& childStyle, ItemPosition resolvedAutoPositionForRenderer);
 
     StyleDifference visualInvalidationDiff(const LayoutStyle&) const;
 
     enum IsAtShadowBoundary {
         AtShadowBoundary,
         NotAtShadowBoundary,
     };
 
     void inheritFrom(const LayoutStyle& inheritParent, IsAtShadowBoundary = NotAtShadowBoundary);
-    void copyNonInheritedFrom(const LayoutStyle&);
+    void copyNonInheritedFromCached(const LayoutStyle&);
 
     PseudoId styleType() const { return static_cast<PseudoId>(noninherited_flags.styleType); }
     void setStyleType(PseudoId styleType) { noninherited_flags.styleType = styleType; }
 
     LayoutStyle* getCachedPseudoStyle(PseudoId) const;
     LayoutStyle* addCachedPseudoStyle(PassRefPtr<LayoutStyle>);
     void removeCachedPseudoStyle(PseudoId);
 
     const PseudoStyleCache* cachedPseudoStyles() const { return m_cachedPseudoStyles.get(); }
 
@@ skipping 1486 matching lines @@
 }
 
 inline bool LayoutStyle::hasPseudoElementStyle() const
 {
     return noninherited_flags.pseudoBits & PSEUDO_ELEMENT_MASK;
 }
 
 } // namespace blink
 
 #endif // LayoutStyle_h