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

Source/core/rendering/RenderNamedFlowThread.cpp

Index: Source/core/rendering/RenderNamedFlowThread.cpp
diff --git a/Source/core/rendering/RenderNamedFlowThread.cpp b/Source/core/rendering/RenderNamedFlowThread.cpp
index 0f64ff51946c4887036b7f5fcb86dce1fd5f63f6..7b958faec9669e017857a4d705dcfaaf30645d6b 100644
--- a/Source/core/rendering/RenderNamedFlowThread.cpp
+++ b/Source/core/rendering/RenderNamedFlowThread.cpp
@@ -90,6 +90,20 @@ void RenderNamedFlowThread::clearContentNodes()
     m_contentNodes.clear();
 }
 
+void RenderNamedFlowThread::updateWritingMode()
+{
+    if (m_regionList.isEmpty())

[mihnea, 2013/07/30 15:50:44]

I believe you want to add an assert here instead. In which situation do you call
this function with an empty region list?

[mstensho (USE GERRIT), 2013/07/31 13:09:37]

If you remove the last region, this list may be empty. But yes, the way the code
is right now, this method isn't even called then. I'm not sure. It's probably a
matter of taste. My idea was that this method should cope also when there are no
regions.

+        return;
+
+    RenderRegion* firstRegion = m_regionList.first();
+    if (style()->writingMode() != firstRegion->style()->writingMode()) {
+        // The first region defines the principal writing mode for the entire flow.
+        RefPtr<RenderStyle> newStyle = RenderStyle::clone(style());
+        newStyle->setWritingMode(firstRegion->style()->writingMode());
+        setStyle(newStyle);
+    }
+}
+
 RenderObject* RenderNamedFlowThread::nextRendererForNode(Node* node) const
 {
     FlowThreadChildList::const_iterator it = m_flowThreadChildList.begin();
@@ -244,6 +258,9 @@ void RenderNamedFlowThread::addRegionToNamedFlowThread(RenderRegion* renderRegio
 
     renderRegion->setIsValid(true);
     addRegionToList(m_regionList, renderRegion);
+
+    if (m_regionList.first() == renderRegion)
+        updateWritingMode();
 }
 
 void RenderNamedFlowThread::addRegionToThread(RenderRegion* renderRegion)
@@ -283,6 +300,7 @@ void RenderNamedFlowThread::removeRegionFromThread(RenderRegion* renderRegion)
     }
 
     ASSERT(m_regionList.contains(renderRegion));
+    bool wasFirst = m_regionList.first() == renderRegion;
     m_regionList.remove(renderRegion);
 
     if (canBeDestroyed())
@@ -291,6 +309,8 @@ void RenderNamedFlowThread::removeRegionFromThread(RenderRegion* renderRegion)
     // After removing all the regions in the flow the following layout needs to dispatch the regionLayoutUpdate event
     if (m_regionList.isEmpty())
         setDispatchRegionLayoutUpdateEvent(true);
+    else if (wasFirst)
+        updateWritingMode();
 
     invalidateRegions();
 }