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 fb82a7c0afc2369dcb56c705915c16ed387d0d39..3090020c1eb529694d5a26df914b7eb4e0f1ba1c 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -4694,6 +4694,11 @@ 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())
+                LayoutBlock::clearPercentHeightDescendantsFrom(postBox);

[mstensho (USE GERRIT), 2016/01/25 09:17:07]

This will process the entire postBox subtree, which could be expensive. But I
assume this is the only safe thing to do?

We could at least avoid some work if we only do this only *once* per
splitAnonymousBoxesAroundChild() call, i.e. do it on the topmost postBox that we
create.

[rhogan, 2016/01/25 19:14:55]

:$

Updated this and the test. Thanks.

+
             beforeChild = postBox;
         } else {
             beforeChild = boxToSplit;