Need a deep layout pass when becoming (un)fragmented.

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 474 matching lines @@
   bool hasSpecifiedPageLogicalHeight = false;
   checkForPaginationLogicalHeightChange(pageLogicalHeight,
                                         pageLogicalHeightChanged,
                                         hasSpecifiedPageLogicalHeight);
   if (pageLogicalHeightChanged)
     relayoutChildren = true;
 
   LayoutState state(*this, locationOffset(), pageLogicalHeight,
                     pageLogicalHeightChanged, logicalWidthChanged);
 
+  if (m_paginationStateChanged) {
+    // We now need a deep layout to clean up struts after pagination, if we
+    // just ceased to be paginated, or, if we just became paginated on the
+    // other hand, we now need the deep layout, to insert pagination struts.
+    m_paginationStateChanged = false;
+    state.setPaginationStateChanged();
+  }
+
   // We use four values, maxTopPos, maxTopNeg, maxBottomPos, and maxBottomNeg,
   // to track our current maximal positive and negative margins. These values
   // are used when we are collapsed with adjacent blocks, so for example, if you
   // have block A and B collapsing together, then you'd take the maximal
   // positive margin from both A and B and subtract it from the maximal negative
   // margin from both A and B to get the true collapsed margin. This algorithm
   // is recursive, so when we finish layout() our block knows its current
   // maximal positive/negative values.
   //
   // Start out by setting our margin values to our current margins. Table cells
@@ skipping 3694 matching lines @@
 
   if (multiColumnFlowThread()) {
     ASSERT(oldStyle);
     if (type != getFlowThreadType(*oldStyle)) {
       // If we're no longer to be multicol/paged, destroy the flow thread. Also
       // destroy it when switching between multicol and paged, since that
       // affects the column set structure (multicol containers may have
       // spanners, paged containers may not).
       multiColumnFlowThread()->evacuateAndDestroy();
       ASSERT(!multiColumnFlowThread());
+      m_paginationStateChanged = true;
     }
   }
 
   if (type == NoFlowThread || multiColumnFlowThread())
     return;
 
   // Ruby elements manage child insertion in a special way, and would mess up
   // insertion of the flow thread. The flow thread needs to be a direct child of
   // the multicol block (|this|).
   if (isRuby())
     return;
 
   // Form controls are replaced content, and are therefore not supposed to
   // support multicol.
   if (isFileUploadControl() || isTextControl() || isListBox())
     return;
 
   LayoutMultiColumnFlowThread* flowThread = createMultiColumnFlowThread(type);
   addChild(flowThread);
+  m_paginationStateChanged = true;
 
   // Check that addChild() put the flow thread as a direct child, and didn't do
   // fancy things.
   ASSERT(flowThread->parent() == this);
 
   flowThread->populate();
   LayoutBlockFlowRareData& rareData = ensureRareData();
   ASSERT(!rareData.m_multiColumnFlowThread);
   rareData.m_multiColumnFlowThread = flowThread;
 }
@@ skipping 299 matching lines @@
   return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }
 
 void LayoutBlockFlow::invalidateDisplayItemClients(
     PaintInvalidationReason invalidationReason) const {
   BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(
       invalidationReason);
 }
 
 }  // namespace blink