Need to reposition an out-of-flow object *before* re-paginating it.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 1175 matching lines @@
     }
     return false;
 }
 
 void LayoutBlock::layoutPositionedObjects(bool relayoutChildren, PositionedLayoutBehavior info)
 {
     TrackedLayoutBoxListHashSet* positionedDescendants = positionedObjects();
     if (!positionedDescendants)
         return;
 
+    bool isPaginated = view()->layoutState()->isPaginated();
+
     for (auto* positionedObject : *positionedDescendants) {
         positionedObject->setMayNeedPaintInvalidation();
 
         SubtreeLayoutScope layoutScope(*positionedObject);
         // A fixed position element with an absolute positioned ancestor has no way of knowing if the latter has changed position. So
         // if this is a fixed position element, mark it for layout if it has an abspos ancestor and needs to move with that ancestor, i.e.
         // it has static position.
         markFixedPositionObjectForLayoutIfNeeded(positionedObject, layoutScope);
         if (info == LayoutOnlyFixedPositionedObjects) {
             positionedObject->layoutIfNeeded();
             continue;
         }
 
         if (!positionedObject->normalChildNeedsLayout() && (relayoutChildren || needsLayoutDueToStaticPosition(positionedObject)))
             layoutScope.setChildNeedsLayout(positionedObject);
 
         // If relayoutChildren is set and the child has percentage padding or an embedded content box, we also need to invalidate the childs pref widths.
         if (relayoutChildren && positionedObject->needsPreferredWidthsRecalculation())
             positionedObject->setPreferredLogicalWidthsDirty(MarkOnlyThis);
 
+        LayoutUnit logicalTopEstimate;
+        bool needsBlockDirectionLocationSetBeforeLayout = isPaginated && !positionedObject->isUnsplittableForPagination();
+        if (needsBlockDirectionLocationSetBeforeLayout) {
+            // Out-of-flow objects are normally positioned after layout (while in-flow objects are
+            // positioned before layout). If the child object is paginated in the same context as
+            // we are, estimate its logical top now. We need to know this up-front, to correctly
+            // evaluate if we need to mark for relayout, and, if our estimate is correct, we'll
+            // even be able to insert correct pagination struts on the first attempt.
+            LogicalExtentComputedValues computedValues;
+            positionedObject->computeLogicalHeight(positionedObject->logicalHeight(), positionedObject->logicalTop(), computedValues);
+            logicalTopEstimate = computedValues.m_position;
+            positionedObject->setLogicalTop(logicalTopEstimate);
+        }
+
         if (!positionedObject->needsLayout())
             positionedObject->markForPaginationRelayoutIfNeeded(layoutScope);
 
         // FIXME: We should be able to do a r->setNeedsPositionedMovementLayout() here instead of a full layout. Need
         // to investigate why it does not trigger the correct invalidations in that case. crbug.com/350756
         if (info == ForcedLayoutAfterContainingBlockMoved)
             positionedObject->setNeedsLayout(LayoutInvalidationReason::AncestorMoved, MarkOnlyThis);
 
         positionedObject->layoutIfNeeded();
+
+        // Lay out again if our estimate was wrong.
+        if (needsBlockDirectionLocationSetBeforeLayout && logicalTopEstimate != logicalTopForChild(*positionedObject))
+            positionedObject->forceChildLayout();
     }
 }
 
 void LayoutBlock::markPositionedObjectsForLayout()
 {
     if (TrackedLayoutBoxListHashSet* positionedDescendants = positionedObjects()) {
         for (auto* descendant : *positionedDescendants)
             descendant->setChildNeedsLayout();
     }
 }
@@ skipping 1621 matching lines @@
 void LayoutBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const LayoutObject* obj) const
 {
     showLayoutObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace blink