[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 68a2a7a939a26b6e8640681602db8cf44afffc1a..c15a33044fe6852acd87042c105a000d6527d88b 100644
--- a/Source/core/rendering/RenderFlowThread.h
+++ b/Source/core/rendering/RenderFlowThread.h
@@ -67,6 +67,21 @@ public:
     // can easily avoid drawing the children directly.
     virtual LayerType layerTypeRequired() const override final { return NormalLayer; }
 
+    virtual bool isColumnSpanner(const RenderObject*) const { return false; }
+
+    // Is the specified renderer a column spanner or inside one?
+    virtual bool isInsideColumnSpanner(const RenderObject*) const { return false; }
+
+    // Enter the specified column spanner for layout.
+    virtual LayoutUnit enterColumnSpanner(RenderBox*, LayoutUnit logicalTop, SubtreeLayoutScope&) { return LayoutUnit(); }
+
+    // Leave the specified column spanner when layout has finished.
+    virtual void leaveColumnSpanner(RenderBox*, LayoutUnit logicalBottom) { }
+
+    virtual void flowThreadDescendantInserted(RenderObject*) { }
+    virtual void flowThreadDescendantWillBeRemoved(RenderObject*) { }
+    virtual void flowThreadDescendantStyleDidChange(RenderObject*) { }
+
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) override final;
 
     virtual void addRegionToThread(RenderMultiColumnSet*) = 0;
@@ -133,9 +148,9 @@ 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)
         {
@@ -145,11 +160,11 @@ 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;
     };
 
     // Stack of objects that pushed a LayoutState object on the RenderView. The