Use LayoutObject to locate the flow thread.

Source/core/paint/DeprecatedPaintLayer.cpp

Index: Source/core/paint/DeprecatedPaintLayer.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayer.cpp b/Source/core/paint/DeprecatedPaintLayer.cpp
index 8167ca351f47d5c7b89ad8c07e566e66749ae215..a7b780e80a783c8f0b4e73aafb666f3e70891dbb 100644
--- a/Source/core/paint/DeprecatedPaintLayer.cpp
+++ b/Source/core/paint/DeprecatedPaintLayer.cpp
@@ -476,37 +476,9 @@ void DeprecatedPaintLayer::updatePagination()
         return;
     }
 
-    if (!m_stackingNode->isTreatedAsStackingContextForPainting()) {
-        // We cannot take the fast path for spanners, as they do not have their nearest ancestor
-        // pagination layer (flow thread) in their containing block chain.
-        if (!layoutObject()->isColumnSpanAll()) {
-            // Content inside a transform is not considered to be paginated, since we simply
-            // paint the transform multiple times in each column, so we don't have to use
-            // fragments for the transformed content.
-            m_enclosingPaginationLayer = parent()->enclosingPaginationLayer();
-            if (m_enclosingPaginationLayer && m_enclosingPaginationLayer->hasTransformRelatedProperty())
-                m_enclosingPaginationLayer = 0;
-            return;
-        }
-    }
-
-    // Walk up our containing block chain looking for an enclosing layer. Once we find one, then we
-    // just check its pagination status.
-    LayoutView* view = layoutObject()->view();
-    LayoutBlock* containingBlock;
-    for (containingBlock = layoutObject()->containingBlock();
-        containingBlock && containingBlock != view;
-        containingBlock = containingBlock->containingBlock()) {
-        if (containingBlock->hasLayer()) {
-            // Content inside a transform is not considered to be paginated, since we simply
-            // paint the transform multiple times in each column, so we don't have to use
-            // fragments for the transformed content.
-            m_enclosingPaginationLayer = containingBlock->layer()->enclosingPaginationLayer();
-            if (m_enclosingPaginationLayer && m_enclosingPaginationLayer->hasTransformRelatedProperty())
-                m_enclosingPaginationLayer = 0;
-            return;
-        }
-    }
+    // Use the layout tree to find our enclosing pagination layer.
+    if (LayoutFlowThread* containingFlowThread = layoutObject()->flowThreadContainingBlock())
+        m_enclosingPaginationLayer = containingFlowThread->layer();

[chrishtr, 2015/07/14 19:57:43]

Should there be code that nulls out m_enclosingPaginationLayer when pagination
goes away?

[mstensho (USE GERRIT), 2015/07/14 20:05:31]

That shouldn't be necessary, since updatePaginationRecursive() (its only caller)
does it.

 }
 
 void DeprecatedPaintLayer::clearPaginationRecursive()