Allow pagination struts to push objects below the exact top of the next column.

third_party/WebKit/Source/core/layout/ColumnBalancer.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/ColumnBalancer.h"
 
 #include "core/layout/LayoutMultiColumnFlowThread.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 #include "core/layout/api/LineLayoutBlockFlow.h"
 
@@ skipping 108 matching lines @@
   return m_contentRuns[index].columnLogicalHeight(startOffset);
 }
 
 void InitialColumnHeightFinder::examineBoxAfterEntering(
     const LayoutBox& box,
     EBreak previousBreakAfterValue) {
   if (isLogicalTopWithinBounds(flowThreadOffset() - box.paginationStrut())) {
     if (box.needsForcedBreakBefore(previousBreakAfterValue)) {
       addContentRun(flowThreadOffset());
     } else {
-      ASSERT(isFirstAfterBreak(flowThreadOffset()) || !box.paginationStrut());
       if (isFirstAfterBreak(flowThreadOffset())) {
         // This box is first after a soft break.
         recordStrutBeforeOffset(flowThreadOffset(), box.paginationStrut());
       }
     }
   }
 
   if (box.getPaginationBreakability() != LayoutBox::AllowAnyBreaks) {
     LayoutUnit unsplittableLogicalHeight = box.logicalHeight();
     if (box.isFloating())
@@ skipping 146 matching lines @@
     const LayoutBox& box,
     EBreak previousBreakAfterValue) {
   LayoutBox::PaginationBreakability breakability =
       box.getPaginationBreakability();
 
   // Look for breaks before the child box.
   if (isLogicalTopWithinBounds(flowThreadOffset() - box.paginationStrut())) {
     if (box.needsForcedBreakBefore(previousBreakAfterValue)) {
       m_forcedBreaksCount++;
     } else {
-      ASSERT(isFirstAfterBreak(flowThreadOffset()) || !box.paginationStrut());
       if (isFirstAfterBreak(flowThreadOffset())) {
         // This box is first after a soft break.
         LayoutUnit strut = box.paginationStrut();
         // Figure out how much more space we would need to prevent it from being
         // pushed to the next column.
         recordSpaceShortage(box.logicalHeight() - strut);
         if (breakability != LayoutBox::ForbidBreaks &&
             m_pendingStrut == LayoutUnit::min()) {
           // We now want to look for the first piece of unbreakable content
           // (e.g. a line or a block-displayed image) inside this block. That
@@ skipping 97 matching lines @@
   if (group.columnLogicalTopForOffset(lineTopInFlowThread) !=
       group.columnLogicalTopForOffset(lineBottomWithOverflow)) {
     LayoutUnit shortage =
         lineBottomWithOverflow -
         group.columnLogicalTopForOffset(lineBottomWithOverflow);
     recordSpaceShortage(shortage);
   }
 }
 
 }  // namespace blink