[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..3382ffe17c1c0ee5f13f4437670ad049745689f2 100644
--- a/Source/core/rendering/RenderFlowThread.h
+++ b/Source/core/rendering/RenderFlowThread.h
@@ -67,6 +67,15 @@ public:
     // can easily avoid drawing the children directly.
     virtual LayerType layerTypeRequired() const OVERRIDE FINAL { return NormalLayer; }
 
+    // Some renderers (column spanners) are moved out of the flow thread to live among column

[Julien - ping for review, 2014/09/03 23:22:22]

I would remove |some renderers| and just put |column spanners| directly.

[mstensho (USE GERRIT), 2014/09/04 12:14:02]

Done.

+    // 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; }
+    // Called when a descendant of the flow thread has been inserted.

[Julien - ping for review, 2014/09/03 23:22:22]

This comment restates exactly what the name of the function says :-(

[mstensho (USE GERRIT), 2014/09/04 12:14:02]

Done.

+    virtual void flowThreadDescendantInserted(RenderObject*) { }
+    // Called when a sibling or descendant of the flow thread is about to be removed.

[Julien - ping for review, 2014/09/03 23:22:22]

Same comment.

[mstensho (USE GERRIT), 2014/09/04 12:14:02]

Done.

+    virtual void flowThreadRelativeWillBeRemoved(RenderObject*) { }
+
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) OVERRIDE FINAL;
 
     virtual void addRegionToThread(RenderMultiColumnSet*) = 0;
@@ -158,9 +167,9 @@ 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 +179,11 @@ 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