[New Multicolumn] Simplified layout also needs to mark spanner placeholders for layout.

Source/core/layout/LayoutBlockFlow.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1989 matching lines @@
                 // Column rules are painted by anonymous column set children of the multicol
                 // container. We need to notify them.
                 flowThread->columnRuleStyleDidChange();
             }
         }
     }
 }
 
 void LayoutBlockFlow::updateBlockChildDirtyBitsBeforeLayout(bool relayoutChildren, LayoutBox& child)
 {
-    if (child.isLayoutMultiColumnSpannerPlaceholder() && toLayoutMultiColumnSpannerPlaceholder(child).layoutObjectInFlowThread()->needsLayout()) {
-        // The containing block of a spanner is the multicol container (|this| block), but the spanner
-        // is laid out via its spanner set (|child|), so we need to make sure that we enter it.
-        child.setChildNeedsLayout(MarkOnlyThis);
-    }
+    if (child.isLayoutMultiColumnSpannerPlaceholder())
+        toLayoutMultiColumnSpannerPlaceholder(child).markForLayoutIfObjectInFlowThreadNeedsLayout();
     LayoutBlock::updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);
 }
 
 void LayoutBlockFlow::updateStaticInlinePositionForChild(LayoutBox& child, LayoutUnit logicalTop)
 {
     if (child.style()->isOriginalDisplayInlineType())
         setStaticInlinePositionForChild(child, startAlignedOffsetForLine(logicalTop, false));
     else
         setStaticInlinePositionForChild(child, startOffsetForContent());
 }
@@ skipping 1159 matching lines @@
     FrameView* frameView = document().view();
     LayoutUnit top = (style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height();
     int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
     if (size().height() < visibleHeight)
         top += (visibleHeight - size().height()) / 2;
     setY(top);
     dialog->setCentered(top);
 }
 
 } // namespace blink