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

Source/core/rendering/RenderRegion.cpp

Index: Source/core/rendering/RenderRegion.cpp
diff --git a/Source/core/rendering/RenderRegion.cpp b/Source/core/rendering/RenderRegion.cpp
index 1952abe9bce747a37a8aaa581c3aa40922a23035..fdc4554dbf436524805736aed7e17a78dcb83137 100644
--- a/Source/core/rendering/RenderRegion.cpp
+++ b/Source/core/rendering/RenderRegion.cpp
@@ -269,6 +269,9 @@ void RenderRegion::styleDidChange(StyleDifference diff, const RenderStyle* oldSt
 
     checkRegionStyle();
     updateRegionHasAutoLogicalHeightFlag();
+
+    if (oldStyle && oldStyle->writingMode() != style()->writingMode())
+        m_flowThread->regionChangedWritingMode(this);
 }
 
 void RenderRegion::layoutBlock(bool relayoutChildren, LayoutUnit)