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

third_party/WebKit/Source/core/style/ComputedStyle.cpp

Index: third_party/WebKit/Source/core/style/ComputedStyle.cpp
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.cpp b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
index 874e929fbcf1e18d199b48bc3f6870a7f744c8fb..1524385a8fc628f29d2cb85dcf01c84620d86f90 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -182,8 +182,7 @@ StyleRecalcChange ComputedStyle::stylePropagationDiff(const ComputedStyle* oldSt
         || 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))
@@ -206,6 +205,17 @@ ItemPosition ComputedStyle::resolveAlignment(const ComputedStyle& parentStyle, c
     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)