Column balancing support in the region based multicol implementation.

Source/core/rendering/RenderBlock.h

Index: Source/core/rendering/RenderBlock.h
diff --git a/Source/core/rendering/RenderBlock.h b/Source/core/rendering/RenderBlock.h
index ce130bf7d6bb746451ac319311819722496b04ae..3a92dae1843b14fc2eca8f1934285ef4b1c801e1 100644
--- a/Source/core/rendering/RenderBlock.h
+++ b/Source/core/rendering/RenderBlock.h
@@ -1098,6 +1098,14 @@ public:
 protected:
     bool pushToNextPageWithMinimumLogicalHeight(LayoutUnit& adjustment, LayoutUnit logicalOffset, LayoutUnit minimumLogicalHeight) const;
 
+    // A page break is required at some offset due to space shortage in the current fragmentainer.
+    void setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage);
+
+    // Update minimum page height required to avoid fragmentation where it shouldn't occur (inside
+    // unbreakable content, between orphans and widows, etc.). This will be used as a hint to the
+    // column balancer to help set a good minimum column height.
+    void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight);
+
     LayoutUnit adjustForUnsplittableChild(RenderBox* child, LayoutUnit logicalOffset, bool includeMargins = false); // If the child is unsplittable and can't fit on the current page, return the top of the next page/column.
     void adjustLinePositionForPagination(RootInlineBox*, LayoutUnit& deltaOffset, RenderFlowThread*); // Computes a deltaOffset value that put a line at the top of the next page if it doesn't fit on the current page.
     LayoutUnit adjustBlockChildForPagination(LayoutUnit logicalTopAfterClear, LayoutUnit estimateWithoutPagination, RenderBox* child, bool atBeforeSideOfBlock);