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

third_party/WebKit/Source/core/style/ComputedStyle.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 164 matching lines @@
     if ((!oldStyle && newStyle) || (oldStyle && !newStyle))
         return Reattach;
 
     if (!oldStyle && !newStyle)
         return NoChange;
 
     if (oldStyle->display() != newStyle->display()
         || oldStyle->hasPseudoStyle(FIRST_LETTER) != newStyle->hasPseudoStyle(FIRST_LETTER)
         || !oldStyle->contentDataEquivalent(newStyle)
         || oldStyle->hasTextCombine() != newStyle->hasTextCombine()
-        || oldStyle->justifyItems() != newStyle->justifyItems()
-        || oldStyle->alignItems() != newStyle->alignItems())
+        || oldStyle->justifyItems() != newStyle->justifyItems())

[esprehn, 2016/01/29 04:20:56]

we need to fix justifyItems too btw (in another patch), it should be very hard
to cause a Reattach

         return Reattach;
 
     if (oldStyle->inheritedNotEqual(*newStyle))
         return Inherit;
 
     if (*oldStyle == *newStyle)
         return diffPseudoStyles(*oldStyle, *newStyle);
 
     if (oldStyle->hasExplicitlyInheritedProperties())
         return Inherit;
 
     return NoInherit;
 }
 
 ItemPosition ComputedStyle::resolveAlignment(const ComputedStyle& parentStyle, const ComputedStyle& childStyle, ItemPosition resolvedAutoPositionForLayoutObject)
 {
     // The auto keyword computes to the parent's align-items computed value, or to "stretch", if not set or "auto".
     if (childStyle.alignSelfPosition() == ItemPositionAuto)
         return (parentStyle.alignItemsPosition() == ItemPositionAuto) ? resolvedAutoPositionForLayoutObject : parentStyle.alignItemsPosition();
     return childStyle.alignSelfPosition();
 }
 
+const StyleSelfAlignmentData ComputedStyle::resolvedAlignment(const ComputedStyle& parentStyle, const ComputedStyle& childStyle, ItemPosition resolvedAutoPositionForLayoutObject)

[esprehn, 2016/01/29 04:20:56]

This should be an instance method on either the child or the parent,

+{
+    // The auto keyword computes to the parent's align-items computed value, or to "stretch", if not set or "auto".
+    if (childStyle.alignSelfPosition() == ItemPositionAuto) {
+        if (parentStyle.alignItemsPosition() == ItemPositionAuto)
+            return {resolvedAutoPositionForLayoutObject, OverflowAlignmentDefault};
+        return parentStyle.alignItems();
+    }
+    return childStyle.alignSelf();
+}
+
 ItemPosition ComputedStyle::resolveJustification(const ComputedStyle& parentStyle, const ComputedStyle& childStyle, ItemPosition resolvedAutoPositionForLayoutObject)
 {
     if (childStyle.justifySelfPosition() == ItemPositionAuto)
         return (parentStyle.justifyItemsPosition() == ItemPositionAuto) ? resolvedAutoPositionForLayoutObject : parentStyle.justifyItemsPosition();
     return childStyle.justifySelfPosition();
 }
 
 void ComputedStyle::inheritFrom(const ComputedStyle& inheritParent, IsAtShadowBoundary isAtShadowBoundary)
 {
     if (isAtShadowBoundary == AtShadowBoundary) {
@@ skipping 1610 matching lines @@
 }
 
 void ComputedStyle::copyChildDependentFlagsFrom(const ComputedStyle& other)
 {
     setEmptyState(other.emptyState());
     if (other.hasExplicitlyInheritedProperties())
         setHasExplicitlyInheritedProperties();
 }
 
 } // namespace blink