collectLayerFragments() expects a dirty rect relative to the multicol container.

Source/core/layout/LayoutFlowThread.cpp

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
@@ skipping 130 matching lines @@
 
 void LayoutFlowThread::generateColumnSetIntervalTree()
 {
     // FIXME: Optimize not to clear the interval all the time. This implies manually managing the tree nodes lifecycle.
     m_multiColumnSetIntervalTree.clear();
     m_multiColumnSetIntervalTree.initIfNeeded();
     for (auto columnSet : m_multiColumnSetList)
         m_multiColumnSetIntervalTree.add(MultiColumnSetIntervalTree::createInterval(columnSet->logicalTopInFlowThread(), columnSet->logicalBottomInFlowThread(), columnSet));
 }
 
-void LayoutFlowThread::collectLayerFragments(DeprecatedPaintLayerFragments& layerFragments, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect)
+void LayoutFlowThread::collectLayerFragments(DeprecatedPaintLayerFragments& layerFragments, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRectInFlowThread)
 {
     ASSERT(!m_columnSetsInvalidated);
 
+    LayoutRect dirtyRectInMulticolContainer(dirtyRectInFlowThread);
+    dirtyRectInMulticolContainer.moveBy(location());
+
     for (LayoutMultiColumnSetList::const_iterator iter = m_multiColumnSetList.begin(); iter != m_multiColumnSetList.end(); ++iter) {
         LayoutMultiColumnSet* columnSet = *iter;
-        columnSet->collectLayerFragments(layerFragments, layerBoundingBox, dirtyRect);
+        columnSet->collectLayerFragments(layerFragments, layerBoundingBox, dirtyRectInMulticolContainer);
     }
 }
 
 LayoutRect LayoutFlowThread::fragmentsBoundingBox(const LayoutRect& layerBoundingBox) const
 {
     ASSERT(!m_columnSetsInvalidated);
 
     LayoutRect result;
     for (auto* columnSet : m_multiColumnSetList) {
         DeprecatedPaintLayerFragments fragments;
@@ skipping 11 matching lines @@
 
 void LayoutFlowThread::MultiColumnSetSearchAdapter::collectIfNeeded(const MultiColumnSetInterval& interval)
 {
     if (m_result)
         return;
     if (interval.low() <= m_offset && interval.high() > m_offset)
         m_result = interval.data();
 }
 
 } // namespace blink