[Slimming paint] [New Multicolumn] Repaint column rules when they change.

Source/core/rendering/RenderBlockFlow.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 1958 matching lines @@
                 }
             }
         }
 
         parentBlockFlow->markAllDescendantsWithFloatsForLayout();
         parentBlockFlow->markSiblingsWithFloatsForLayout();
     }
 
     if (diff.needsFullLayout() || !oldStyle)
         createOrDestroyMultiColumnFlowThreadIfNeeded(oldStyle);
+    if (oldStyle) {
+        if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
+            if (!style()->columnRuleEquivalent(oldStyle)) {
+                // Column rules are painted by anonymous column set children of the multicol
+                // container. We need to notify them.
+                flowThread->columnRuleStyleDidChange();
+            }
+        }
+    }
 }
 
 void RenderBlockFlow::updateBlockChildDirtyBitsBeforeLayout(bool relayoutChildren, RenderBox& child)
 {
     if (child.isRenderMultiColumnSpannerPlaceholder() && toRenderMultiColumnSpannerPlaceholder(child).rendererInFlowThread()->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);
     }
     RenderBlock::updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);
@@ skipping 1132 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