Clear box from percentage descendants when it is split off from the ancestor

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 2348ba690993427266953fde54c7023a018e0497..9ebcb1dc5ebecfdd51c3423e728e9039bafea809 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -4658,9 +4658,16 @@ LayoutObject* LayoutBox::splitAnonymousBoxesAroundChild(LayoutObject* beforeChil
             markBoxForRelayoutAfterSplit(boxToSplit);
             markBoxForRelayoutAfterSplit(postBox);
 
+            // Splitting the box means the left side of the container chain will lose any percent height descendants
+            // below |postBox| in the right hand side.
+            if (LayoutBlock::hasPercentHeightContainerMap())

[mstensho (USE GERRIT), 2016/01/18 20:06:24]

Can this be moved to a separate CL? This change isn't mentioned in the
description. If everything really has to be done in one and the same CL (not
that it's a lot, but it's two things, nonetheless), better update the
description.

[mstensho (USE GERRIT), 2016/01/21 19:12:32]

Well? :)

+                LayoutBlock::clearPercentHeightDescendantsFrom(postBox);
+
             beforeChild = postBox;
         } else {
-            beforeChild = boxToSplit;
+            // If a lone anonymous block is now unnecessary. Collapse it away and skip to its parent.

[mstensho (USE GERRIT), 2016/01/18 20:06:24]

"If" without "then". :-P

Did you mean to write this in one sentence? "... unnecessary, collapse ..."

+            if (!boxToSplit->isLayoutBlock() || !toLayoutBlock(boxToSplit)->collapseLoneAnonymousBlock(toLayoutBlock(boxToSplit)))

[mstensho (USE GERRIT), 2016/01/18 20:06:24]

I hope collapseLoneAnonymousBlock() can be static. This looks silly. :)

+                beforeChild = boxToSplit;
         }

[mstensho (USE GERRIT), 2016/01/18 20:06:24]

What if collapseLoneAnonymousBlock() did something here and returned true? Then
|beforeChild| isn't updated. Aren't you going to get stuck in this loop then?

     }