[New Multicolumn] Actual support for layout of 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 74a6b9cb50c34fa38658469ba0c5b208af1935e2..1962f32c38d42acaa4b849198a2d1046bcf0b416 100644
--- a/Source/core/rendering/RenderFlowThread.h
+++ b/Source/core/rendering/RenderFlowThread.h
@@ -58,7 +58,6 @@ public:
     virtual ~RenderFlowThread() { };
 
     virtual bool isRenderFlowThread() const override final { return true; }
-    virtual bool isRenderMultiColumnFlowThread() const { return false; }
     virtual bool isRenderPagedFlowThread() const { return false; }
 
     virtual void layout() override;
@@ -67,7 +66,15 @@ 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; }
+
+    virtual LayoutUnit enterColumnSpannerBeforeLayout(RenderBox*, LayoutUnit logicalTop, SubtreeLayoutScope&) { return LayoutUnit(); }
+    virtual void leaveColumnSpannerAfterLayout(RenderBox*, LayoutUnit logicalBottom) { }

[Julien - ping for review, 2014/11/19 17:54:34]

A better antonym of enter is "exit". At least that's what is written everywhere
in shops ;)

[mstensho (USE GERRIT), 2014/11/21 15:39:24]

I think I enter and leave shops all the time, but maybe that's something you can
only do here in this non-English-speaking country. :)

Anyway: Done.

[Julien - ping for review, 2014/11/26 21:09:00]

Official leave sign:
http://squamcreativeservices.files.wordpress.com/2012/08/squam-creative-teele...
;-)

     virtual void flowThreadDescendantWasInserted(RenderObject*) { }
+    virtual void flowThreadDescendantWillBeRemoved(RenderObject*) { }
 
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) override final;
 
@@ -116,14 +123,14 @@ public:
     // Used to estimate the maximum height of the flow thread.
     static LayoutUnit maxLogicalHeight() { return LayoutUnit::max() / 2; }
 
+    virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const = 0;
+
 protected:
     virtual const char* renderName() const = 0;
 
     void updateRegionsFlowThreadPortionRect();
     bool shouldIssuePaintInvalidations(const LayoutRect&) const;
 
-    virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const = 0;
-
     bool cachedOffsetFromLogicalTopOfFirstRegion(const RenderBox*, LayoutUnit&) const;
     void setOffsetFromLogicalTopOfFirstRegion(const RenderBox*, LayoutUnit);
     void clearOffsetFromLogicalTopOfFirstRegion(const RenderBox*);
@@ -135,9 +142,9 @@ 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)
         {
@@ -147,11 +154,11 @@ 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