Add support for the column-fill property.

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index fbd1d494c7b239d82916e9157fdf4fbe33c34109..b758cdfa0459b33f084493eb8e4d9ca14a8c1687 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -6488,8 +6488,13 @@ void RenderBlock::adjustLinePositionForPagination(RootInlineBox* lineBox, Layout
             lineBox->setPaginationStrut(remainingLogicalHeight);
             lineBox->setIsFirstAfterPageBreak(true);
         }
-    } else if (remainingLogicalHeight == pageLogicalHeight && lineBox != firstRootBox())
-        lineBox->setIsFirstAfterPageBreak(true);
+    } else if (remainingLogicalHeight == pageLogicalHeight) {
+        // We're at the very top of a page or column.
+        if (lineBox != firstRootBox())
+            lineBox->setIsFirstAfterPageBreak(true);
+        if (lineBox != firstRootBox() || offsetFromLogicalTopOfFirstPage())
+            setPageBreak(logicalOffset, lineHeight);
+    }
 }
 
 bool RenderBlock::lineWidthForPaginatedLineChanged(RootInlineBox* rootBox, LayoutUnit lineDelta, RenderFlowThread* flowThread) const