Append fragmentainer groups in outer multicols first.

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

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 492 matching lines @@
     }
 
     if (!columnSet->hasFragmentainerGroupForColumnAt(offsetInFlowThread, pageBoundaryRule)) {
         FragmentationContext* enclosingFragmentationContext = this->enclosingFragmentationContext();
         if (!enclosingFragmentationContext)
             return; // Not nested. We'll never need more rows than the one we already have then.
         ASSERT(!isLayoutPagedFlowThread());
 
         // We have run out of columns here, so we need to add at least one more row to hold more
         // columns.
+        LayoutMultiColumnFlowThread* enclosingFlowThread = enclosingFragmentationContext->associatedFlowThread();
         do {
+            if (enclosingFlowThread) {
+                // When we add a new row here, it implicitly means that we're inserting another
+                // column in our enclosing multicol container. That in turn may mean that we've run
+                // out of columns there too. Need to insert additional rows in ancestral multicol
+                // containers before doing it in the descendants, in order to get the height
+                // constraints right down there.
+                const MultiColumnFragmentainerGroup& lastRow = columnSet->lastFragmentainerGroup();
+                // The top offset where where the new fragmentainer group will start in this column
+                // set, converted to the coordinate space of the enclosing multicol container.
+                LayoutUnit logicalOffsetInOuter = lastRow.blockOffsetInEnclosingFragmentationContext() + lastRow.logicalHeight();
+                enclosingFlowThread->appendNewFragmentainerGroupIfNeeded(logicalOffsetInOuter, AssociateWithLatterPage);
+            }
+
             const MultiColumnFragmentainerGroup& newRow = columnSet->appendNewFragmentainerGroup();
             // Zero-height rows should really not occur here, but if it does anyway, break, so that
             // we don't get stuck in an infinite loop.
             ASSERT(newRow.logicalHeight() > 0);
             if (newRow.logicalHeight() <= 0)
                 break;
         } while (!columnSet->hasFragmentainerGroupForColumnAt(offsetInFlowThread, pageBoundaryRule));
-
-        if (LayoutMultiColumnFlowThread* enclosingFlowThread = enclosingFragmentationContext->associatedFlowThread()) {
-            // When we add a new row here, it implicitly means that we're inserting another column
-            // in our enclosing multicol container. That in turn may mean that we've run out of
-            // columns there too.
-            const MultiColumnFragmentainerGroup& lastRow = columnSet->lastFragmentainerGroup();
-            enclosingFlowThread->appendNewFragmentainerGroupIfNeeded(lastRow.blockOffsetInEnclosingFragmentationContext(), AssociateWithLatterPage);
-        }
     }
 }
 
 bool LayoutMultiColumnFlowThread::isFragmentainerLogicalHeightKnown()
 {
     return isPageLogicalHeightKnown();
 }
 
 LayoutUnit LayoutMultiColumnFlowThread::fragmentainerLogicalHeightAt(LayoutUnit blockOffset)
 {
@@ skipping 475 matching lines @@
         }
         if (canContainSpannerInParentFragmentationContext(*object))
             next = object->nextInPreOrder(&root);
         else
             next = object->nextInPreOrderAfterChildren(&root);
     }
     return true;
 }
 
 } // namespace blink