Allow zero-height fragmentainers.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/MultiColumnFragmentainerGroup.h"
 
 #include "core/layout/ColumnBalancer.h"
 #include "core/layout/FragmentationContext.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 
@@ skipping 308 matching lines @@
   LayoutUnit maxColumnHeight = flowThread->maxColumnLogicalHeight();
   LayoutUnit maxHeight = heightAdjustedForRowOffset(maxColumnHeight);
   if (FragmentationContext* enclosingFragmentationContext =
           flowThread->enclosingFragmentationContext()) {
     if (enclosingFragmentationContext->isFragmentainerLogicalHeightKnown()) {
       // We're nested inside another fragmentation context whose fragmentainer
       // heights are known. This constrains the max height.
       LayoutUnit remainingOuterLogicalHeight =
           enclosingFragmentationContext->remainingLogicalHeightAt(
               blockOffsetInEnclosingFragmentationContext());
-      ASSERT(remainingOuterLogicalHeight > 0);
       if (maxHeight > remainingOuterLogicalHeight)
         maxHeight = remainingOuterLogicalHeight;
     }
   }
   return maxHeight;
 }
 
 void MultiColumnFragmentainerGroup::setAndConstrainColumnHeight(
     LayoutUnit newHeight) {
   m_columnHeight = newHeight;
@@ skipping 254 matching lines @@
 MultiColumnFragmentainerGroupList::addExtraGroup() {
   append(MultiColumnFragmentainerGroup(m_columnSet));
   return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups() {
   shrink(1);
 }
 
 }  // namespace blink