Prepare height calculation methods in LayoutFlowThread for nested multicol.

Source/core/layout/LayoutMultiColumnSet.h

Index: Source/core/layout/LayoutMultiColumnSet.h
diff --git a/Source/core/layout/LayoutMultiColumnSet.h b/Source/core/layout/LayoutMultiColumnSet.h
index 0eecd1453b7e025f7eb2b5df004f49f61c491b0b..1d189ebbfb2565d6de234fc65222f8e602307bb7 100644
--- a/Source/core/layout/LayoutMultiColumnSet.h
+++ b/Source/core/layout/LayoutMultiColumnSet.h
@@ -73,7 +73,9 @@ public:
 
     // Return the width and height of a single column or page in the set.
     LayoutUnit pageLogicalWidth() const { return flowThread()->logicalWidth(); }
-    LayoutUnit pageLogicalHeight() const;
+    LayoutUnit pageLogicalHeightForOffset(LayoutUnit) const;
+    LayoutUnit pageRemainingLogicalHeightForOffset(LayoutUnit, PageBoundaryRule) const;
+    bool isPageLogicalHeightKnown() const;
 
     LayoutFlowThread* flowThread() const { return m_flowThread; }