[New Multicolumn] Add support for column-span:all

Source/core/rendering/RenderFlowThread.h

Index: Source/core/rendering/RenderFlowThread.h
diff --git a/Source/core/rendering/RenderFlowThread.h b/Source/core/rendering/RenderFlowThread.h
index 127edc4e01a4d82fe6b4b20f182eedb382fa6ba8..9f2bca1e720b9304d2ed3738ad430dad33994e9c 100644
--- a/Source/core/rendering/RenderFlowThread.h
+++ b/Source/core/rendering/RenderFlowThread.h
@@ -67,6 +67,14 @@ public:
     // can easily avoid drawing the children directly.
     virtual LayerType layerTypeRequired() const OVERRIDE FINAL { return NormalLayer; }
 
+    // Column spanners are moved out of the flow thread to live among column sets. If |child| is
+    // such a renderer, resolve it to the placeholder that lives at the original location in the
+    // tree.
+    virtual RenderObject* resolveMovedChild(RenderObject* child) const { return child; }
+
+    virtual void flowThreadDescendantInserted(RenderObject*) { }
+    virtual void flowThreadDescendantOrSiblingWillBeRemoved(RenderObject*) { }
+
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) OVERRIDE FINAL;
 
     virtual void addRegionToThread(RenderMultiColumnSet*) = 0;
@@ -158,9 +166,9 @@ protected:
     typedef PODInterval<LayoutUnit, RenderMultiColumnSet*> MultiColumnSetInterval;
     typedef PODIntervalTree<LayoutUnit, RenderMultiColumnSet*> MultiColumnSetIntervalTree;
 
-    class RegionSearchAdapter {
+    class MultiColumnSetSearchAdapter {
     public:
-        RegionSearchAdapter(LayoutUnit offset)
+        MultiColumnSetSearchAdapter(LayoutUnit offset)
             : m_offset(offset)
             , m_result(0)
         {
@@ -170,11 +178,11 @@ protected:
         const LayoutUnit& highValue() const { return m_offset; }
         void collectIfNeeded(const MultiColumnSetInterval&);
 
-        RenderRegion* result() const { return m_result; }
+        RenderMultiColumnSet* result() const { return m_result; }
 
     private:
         LayoutUnit m_offset;
-        RenderRegion* m_result;
+        RenderMultiColumnSet* m_result;
     };
 
     // A maps from RenderBox