[New Multicolumn] Disallow multicol on ruby elements.

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 3081 matching lines @@
             // when switching between multicol and paged, since that affects the column set
             // structure (multicol containers may have spanners, paged containers may not).
             multiColumnFlowThread()->evacuateAndDestroy();
             ASSERT(!multiColumnFlowThread());
         }
     }
 
     if (type == NoFlowThread || multiColumnFlowThread())
         return;
 
+    // Ruby elements manage child insertion in a special way, and would mess up insertion of the
+    // flow thread. The flow thread needs to be a direct child of the multicol block (|this|).
+    if (isRuby())
+        return;
+
     LayoutMultiColumnFlowThread* flowThread = createMultiColumnFlowThread(type);
     addChild(flowThread);
+
+    // Check that addChild() put the flow thread as a direct child, and didn't do fancy things.
+    ASSERT(flowThread->parent() == this);
+
     flowThread->populate();
     LayoutBlockFlowRareData& rareData = ensureRareData();
     ASSERT(!rareData.m_multiColumnFlowThread);
     rareData.m_multiColumnFlowThread = flowThread;
 }
 
 LayoutBlockFlow::LayoutBlockFlowRareData& LayoutBlockFlow::ensureRareData()
 {
     if (m_rareData)
         return *m_rareData;
@@ skipping 47 matching lines @@
     }
     if (isAnonymous())
         return "LayoutBlockFlow (anonymous)";
     if (isRelPositioned())
         return "LayoutBlockFlow (relative positioned)";
     return "LayoutBlockFlow";
 }
 
 
 } // namespace blink