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 24f3f026f6c14b1e10536b4590f4c9f3dfa0b941..c5658c36751ff2f6c6c896eaf30523379bea4b87 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -6474,8 +6474,13 @@ 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