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

Source/core/rendering/RenderRegion.cpp

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
@@ skipping 251 matching lines @@
     // If the region is not attached to any thread, there is no need to check
     // whether the region has region styling since no content will be displayed
     // into the region.
     if (!m_flowThread) {
         setHasCustomRegionStyle(false);
         return;
     }
 
     checkRegionStyle();
     updateRegionHasAutoLogicalHeightFlag();
+
+    if (oldStyle && oldStyle->writingMode() != style()->writingMode())
+        m_flowThread->regionChangedWritingMode(this);
 }
 
 void RenderRegion::layoutBlock(bool relayoutChildren, LayoutUnit)
 {
     StackStats::LayoutCheckPoint layoutCheckPoint;
     RenderBlock::layoutBlock(relayoutChildren);
 
     if (isValid()) {
         LayoutRect oldRegionRect(flowThreadPortionRect());
         if (!isHorizontalWritingMode())
@@ skipping 357 matching lines @@
     if (!hasOverrideHeight())
         return;
 
     LayoutUnit newLogicalHeight = overrideLogicalContentHeight() + borderAndPaddingLogicalHeight();
     ASSERT(newLogicalHeight < LayoutUnit::max() / 2);
     if (newLogicalHeight > logicalHeight())
         setLogicalHeight(newLogicalHeight);
 }
 
 } // namespace WebCore