Keep block pagination struts after layout, and store them before any type of break.

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 e8f4a0ee396646b8273bf9ef8a6d0bd8a0d006c0..ce94f8884c9476fb7cb752086efc480ad626da6b 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1770,6 +1770,13 @@ void LayoutBox::clearSpannerPlaceholder()
     m_rareData->m_spannerPlaceholder = nullptr;
 }
 
+void LayoutBox::setPaginationStrut(LayoutUnit strut)
+{
+    if (!strut && !m_rareData)
+        return;
+    ensureRareData().m_paginationStrut = strut;
+}
+
 LayoutRect LayoutBox::clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* paintInvalidationState) const
 {
     if (style()->visibility() != VISIBLE) {