Add a runtime flag for the column-fill property.

Source/core/style/ComputedStyle.h

Index: Source/core/style/ComputedStyle.h
diff --git a/Source/core/style/ComputedStyle.h b/Source/core/style/ComputedStyle.h
index 64abb5eb0ef055f4949c15f8119748e51432bb07..e84a6fb3ebc4323fe8d4bc7efbf6ebeece15f699 100644
--- a/Source/core/style/ComputedStyle.h
+++ b/Source/core/style/ComputedStyle.h
@@ -1614,7 +1614,7 @@ public:
     static Order initialRTLOrdering() { return LogicalOrder; }
     static float initialTextStrokeWidth() { return 0; }
     static unsigned short initialColumnCount() { return 1; }
-    static ColumnFill initialColumnFill() { return ColumnFillBalance; }
+    static ColumnFill initialColumnFill();
     static ColumnSpan initialColumnSpan() { return ColumnSpanNone; }
     static const TransformOperations& initialTransform() { DEFINE_STATIC_LOCAL(TransformOperations, ops, ()); return ops; }
     static Length initialTransformOriginX() { return Length(50.0, Percent); }