Propagate writing-mode from the first region to the flow thread.

Source/core/rendering/RenderNamedFlowThread.h

 /*
  * Copyright (C) 2012 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 86 matching lines @@
     void removeDependencyOnFlowThread(RenderNamedFlowThread*);
 
     void addRegionToNamedFlowThread(RenderRegion*);
 
     void checkInvalidRegions();
 
     bool canBeDestroyed() const { return m_invalidRegionList.isEmpty() && m_regionList.isEmpty() && m_contentNodes.isEmpty(); }
     void regionLayoutUpdateEventTimerFired(Timer<RenderNamedFlowThread>*);
     void regionOversetChangeEventTimerFired(Timer<RenderNamedFlowThread>*);
     void clearContentNodes();
+    void updateWritingMode();
 
 private:
     // Observer flow threads have invalid regions that depend on the state of this thread
     // to re-validate their regions. Keeping a set of observer threads make it easy
     // to notify them when a region was removed from this flow.
     RenderNamedFlowThreadCountedSet m_observerThreadsSet;
 
     // Some threads need to have a complete layout before we layout this flow.
     // That's because they contain a RenderRegion that should display this thread. The set makes it
     // easy to sort the order of threads layout.
@@ skipping 28 matching lines @@
     return static_cast<const RenderNamedFlowThread*>(object);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toRenderNamedFlowThread(const RenderNamedFlowThread*);
 
 } // namespace WebCore
 
 #endif // RenderNamedFlowThread_h