If an object's containing block is in a flow thread, so is the object.

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

Index: third_party/WebKit/Source/core/layout/LayoutState.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutState.cpp b/third_party/WebKit/Source/core/layout/LayoutState.cpp
index 53c60e6e72c9106ccae8a8dc5c95d6f8ebaf3679..f3510951de593dd49d0c9924caeac2baefdf45ba 100644
--- a/third_party/WebKit/Source/core/layout/LayoutState.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutState.cpp
@@ -52,10 +52,8 @@ LayoutState::LayoutState(LayoutBox& layoutObject,
       m_layoutObject(layoutObject) {
   if (layoutObject.isLayoutFlowThread())
     m_flowThread = toLayoutFlowThread(&layoutObject);
-  else if (!layoutObject.isOutOfFlowPositioned())
-    m_flowThread = m_next->flowThread();
   else
-    m_flowThread = nullptr;
+    m_flowThread = m_next->flowThread();
   m_paginationStateChanged = m_next->m_paginationStateChanged;
   layoutObject.view()->pushLayoutState(*this);
   m_heightOffsetForTableHeaders = m_next->heightOffsetForTableHeaders();