Stop explicit inheritance if LayoutStyle doesn't change.

Source/core/layout/style/LayoutStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
  *
@@ skipping 170 matching lines @@
 
     if (oldStyle->display() != newStyle->display()
         || oldStyle->hasPseudoStyle(FIRST_LETTER) != newStyle->hasPseudoStyle(FIRST_LETTER)
         || oldStyle->columnSpan() != newStyle->columnSpan()
         || !oldStyle->contentDataEquivalent(newStyle)
         || oldStyle->hasTextCombine() != newStyle->hasTextCombine()
         || oldStyle->justifyItems() != newStyle->justifyItems()
         || oldStyle->alignItems() != newStyle->alignItems())
         return Reattach;
 
-    if (oldStyle->inheritedNotEqual(*newStyle)
-        || oldStyle->hasExplicitlyInheritedProperties()
-        || newStyle->hasExplicitlyInheritedProperties())
+    if (oldStyle->inheritedNotEqual(*newStyle))
         return Inherit;
 
     if (*oldStyle == *newStyle)
         return diffPseudoStyles(*oldStyle, *newStyle);
 
+    if (oldStyle->hasExplicitlyInheritedProperties())
+        return Inherit;
+
     return NoInherit;
 }
 
 ItemPosition LayoutStyle::resolveAlignment(const LayoutStyle& parentStyle, const LayoutStyle& childStyle, ItemPosition resolvedAutoPositionForRenderer)
 {
     // The auto keyword computes to the parent's align-items computed value, or to "stretch", if not set or "auto".
     if (childStyle.alignSelf() == ItemPositionAuto)
         return (parentStyle.alignItems() == ItemPositionAuto) ? resolvedAutoPositionForRenderer : parentStyle.alignItems();
     return childStyle.alignSelf();
 }
@@ skipping 35 matching lines @@
     noninherited_flags.overflowY = other.noninherited_flags.overflowY;
     noninherited_flags.verticalAlign = other.noninherited_flags.verticalAlign;
     noninherited_flags.clear = other.noninherited_flags.clear;
     noninherited_flags.position = other.noninherited_flags.position;
     noninherited_flags.floating = other.noninherited_flags.floating;
     noninherited_flags.tableLayout = other.noninherited_flags.tableLayout;
     noninherited_flags.unicodeBidi = other.noninherited_flags.unicodeBidi;
     noninherited_flags.pageBreakBefore = other.noninherited_flags.pageBreakBefore;
     noninherited_flags.pageBreakAfter = other.noninherited_flags.pageBreakAfter;
     noninherited_flags.pageBreakInside = other.noninherited_flags.pageBreakInside;
-    noninherited_flags.explicitInheritance = other.noninherited_flags.explicitInheritance;

[esprehn, 2015/02/13 02:29:13]

Why is it okay not to copy this bit? This seems to break the contract of what
copyNonInheritedFrom does?

     noninherited_flags.hasViewportUnits = other.noninherited_flags.hasViewportUnits;
     if (m_svgStyle != other.m_svgStyle)
         m_svgStyle.access()->copyNonInheritedFrom(other.m_svgStyle.get());
     ASSERT(zoom() == initialZoom());
 }
 
 bool LayoutStyle::operator==(const LayoutStyle& o) const
 {
     // compare everything except the pseudoStyle pointer
     return inherited_flags == o.inherited_flags
@@ skipping 1401 matching lines @@
         horizontal || includeLogicalRightEdge);
 
     edges[BSLeft] = BorderEdge(borderLeftWidth(),
         visitedDependentColor(CSSPropertyBorderLeftColor),
         borderLeftStyle(),
         borderLeftIsTransparent(),
         !horizontal || includeLogicalLeftEdge);
 }
 
 } // namespace blink