Avoid stretching the parent of a column spanner.

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 563 matching lines @@
 {
     // Detach all column sets from the flow thread. Cannot destroy them at this point, since they
     // are siblings of this object, and there may be pointers to this object's sibling somewhere
     // further up on the call stack.
     for (LayoutMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet())
         columnSet->detachFromFlowThread();
     multiColumnBlockFlow()->resetMultiColumnFlowThread();
     LayoutFlowThread::willBeRemovedFromTree();
 }
 
-LayoutUnit LayoutMultiColumnFlowThread::skipColumnSpanner(LayoutBox* layoutObject, LayoutUnit logicalTopInFlowThread)
+void LayoutMultiColumnFlowThread::skipColumnSpanner(LayoutBox* layoutObject, LayoutUnit logicalTopInFlowThread)
 {
     ASSERT(layoutObject->isColumnSpanAll());
     LayoutMultiColumnSpannerPlaceholder* placeholder = layoutObject->spannerPlaceholder();
-    LayoutUnit adjustment;
     LayoutBox* previousColumnBox = placeholder->previousSiblingMultiColumnBox();
-    if (previousColumnBox && previousColumnBox->isLayoutMultiColumnSet()) {
-        // Pad flow thread offset to a column boundary, so that any column content that's supposed
-        // to come after the spanner doesn't bleed into the column row preceding the spanner.
-        LayoutMultiColumnSet* previousSet = toLayoutMultiColumnSet(previousColumnBox);
-        if (previousSet->pageLogicalHeight()) {
-            LayoutUnit columnLogicalTopInFlowThread = previousSet->pageLogicalTopForOffset(logicalTopInFlowThread);
-            if (columnLogicalTopInFlowThread != logicalTopInFlowThread) {
-                adjustment = columnLogicalTopInFlowThread + previousSet->pageLogicalHeight() - logicalTopInFlowThread;
-                logicalTopInFlowThread += adjustment;
-            }
-        }
-        previousSet->endFlow(logicalTopInFlowThread);
-    }
+    if (previousColumnBox && previousColumnBox->isLayoutMultiColumnSet())
+        toLayoutMultiColumnSet(previousColumnBox)->endFlow(logicalTopInFlowThread);
     LayoutBox* nextColumnBox = placeholder->nextSiblingMultiColumnBox();
     if (nextColumnBox && nextColumnBox->isLayoutMultiColumnSet()) {
         LayoutMultiColumnSet* nextSet = toLayoutMultiColumnSet(nextColumnBox);
         m_lastSetWorkedOn = nextSet;
         nextSet->beginFlow(logicalTopInFlowThread);
     }
 
     // We'll lay out of spanners after flow thread layout has finished (during layout of the spanner
     // placeholders). There may be containing blocks for out-of-flow positioned descendants of the
     // spanner in the flow thread, so that out-of-flow objects inside the spanner will be laid out
     // as part of flow thread layout (even if the spanner itself won't). We need to add such
     // out-of-flow positioned objects to their containing blocks now, or they'll never get laid
     // out. Since it's non-trivial to determine if we need this, and where such out-of-flow objects
     // might be, just go through the whole subtree.
     for (LayoutObject* descendant = layoutObject->slowFirstChild(); descendant; descendant = descendant->nextInPreOrder()) {
         if (descendant->isBox() && descendant->isOutOfFlowPositioned())
             descendant->containingBlock()->insertPositionedObject(toLayoutBox(descendant));
     }
-
-    return adjustment;
 }
 
 // When processing layout objects to remove or when processing layout objects that have just been
 // inserted, certain types of objects should be skipped.
 static bool shouldSkipInsertedOrRemovedChild(LayoutMultiColumnFlowThread* flowThread, const LayoutObject& child)
 {
     if (child.isSVG() && !child.isSVGRoot()) {
         // Don't descend into SVG objects. What's in there is of no interest, and there might even
         // be a foreignObject there with column-span:all, which doesn't apply to us.
         return true;
@@ skipping 263 matching lines @@
 }
 
 bool LayoutMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
     if (LayoutMultiColumnSet* columnSet = lastMultiColumnSet())
         return columnSet->pageLogicalHeight();
     return false;
 }
 
 }