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

Source/core/layout/LayoutFlowThread.cpp

Index: Source/core/layout/LayoutFlowThread.cpp
diff --git a/Source/core/layout/LayoutFlowThread.cpp b/Source/core/layout/LayoutFlowThread.cpp
index eca6be0a82beb3cdf1e5ac23ace3cd6fe37073cf..34e5d7793c5f95f03bd9b7239199d10e45d43fa7 100644
--- a/Source/core/layout/LayoutFlowThread.cpp
+++ b/Source/core/layout/LayoutFlowThread.cpp
@@ -148,13 +148,16 @@ void LayoutFlowThread::generateColumnSetIntervalTree()
         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);
     }
 }