[css-align] Avoid the style Reattach whenever align-items changes.

third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ skipping 1590 matching lines @@
         return cssValuePool().createValue(style.direction());
     case CSSPropertyDisplay:
         return cssValuePool().createValue(style.display());
     case CSSPropertyEmptyCells:
         return cssValuePool().createValue(style.emptyCells());
     case CSSPropertyAlignContent:
         return valueForContentPositionAndDistributionWithOverflowAlignment(resolveAlignContentAuto(style));
     case CSSPropertyAlignItems:
         return valueForItemPositionWithOverflowAlignment(resolveAlignmentAuto(style.alignItemsPosition(), &style), style.alignItemsOverflowAlignment(), NonLegacyPosition);
     case CSSPropertyAlignSelf: {
-        Node* parent = styledNode->parentNode();
-        return valueForItemPositionWithOverflowAlignment(resolveAlignmentAuto(style.alignSelfPosition(), parent ? parent->ensureComputedStyle() : nullptr), style.alignSelfOverflowAlignment(), NonLegacyPosition);
+        ItemPosition position = style.alignSelfPosition();
+        if (position == ItemPositionAuto) {
+            const ComputedStyle* parentStyle = styledNode->parentNode() ? styledNode->parentNode()->ensureComputedStyle() : nullptr;

[esprehn, 2016/01/29 04:20:55]

You need to use LayoutTreeBuilderTraversal::parent here, this is broken for
shadow dom. See Node::parentComputedStyle.

I guess this code was already broken, please add a TODO here.

+            position = parentStyle ? ComputedStyle::resolveAlignment(*parentStyle, style, resolveAlignmentAuto(parentStyle->alignItemsPosition(), parentStyle)) : ItemPositionStart;
+        }
+        return valueForItemPositionWithOverflowAlignment(position, style.alignSelfOverflowAlignment(), NonLegacyPosition);
     }
     case CSSPropertyFlex:
         return valuesForShorthandProperty(flexShorthand(), style, layoutObject, styledNode, allowVisitedStyle);
     case CSSPropertyFlexBasis:
         return zoomAdjustedPixelValueForLength(style.flexBasis(), style);
     case CSSPropertyFlexDirection:
         return cssValuePool().createValue(style.flexDirection());
     case CSSPropertyFlexFlow:
         return valuesForShorthandProperty(flexFlowShorthand(), style, layoutObject, styledNode, allowVisitedStyle);
     case CSSPropertyFlexGrow:
@@ skipping 1111 matching lines @@
     case CSSPropertyAll:
         return nullptr;
     default:
         break;
     }
     ASSERT_NOT_REACHED();
     return nullptr;
 }
 
 }