Remove CSS regions support, keeping a bare minimum to support "region-based" multicol.

Source/core/rendering/RootInlineBox.h

Index: Source/core/rendering/RootInlineBox.h
diff --git a/Source/core/rendering/RootInlineBox.h b/Source/core/rendering/RootInlineBox.h
index 2cc1de180acb9fe8b9878827acae1f63397ce0ea..92ea13091364096a42a5038ace84a5e3a89a1bb8 100644
--- a/Source/core/rendering/RootInlineBox.h
+++ b/Source/core/rendering/RootInlineBox.h
@@ -29,7 +29,6 @@ namespace WebCore {
 class EllipsisBox;
 class HitTestResult;
 class RenderBlockFlow;
-class RenderRegion;
 
 struct BidiStatus;
 struct GapRects;
@@ -64,9 +63,6 @@ public:
     LayoutUnit paginatedLineWidth() const { return m_fragmentationData ? m_fragmentationData->m_paginatedLineWidth : LayoutUnit(0); }
     void setPaginatedLineWidth(LayoutUnit width) { ensureLineFragmentationData()->m_paginatedLineWidth = width; }
 
-    RenderRegion* containingRegion() const;
-    void setContainingRegion(RenderRegion*);
-
     LayoutUnit selectionTop() const;
     LayoutUnit selectionBottom() const;
     LayoutUnit selectionHeight() const { return max<LayoutUnit>(0, selectionBottom() - selectionTop()); }
@@ -221,17 +217,13 @@ private:
         WTF_MAKE_NONCOPYABLE(LineFragmentationData); WTF_MAKE_FAST_ALLOCATED;
     public:
         LineFragmentationData()
-            : m_containingRegion(0)
-            , m_paginationStrut(0)
+            : m_paginationStrut(0)
             , m_paginatedLineWidth(0)
             , m_isFirstAfterPageBreak(false)
         {
 
         }
 
-        // It should not be assumed the |containingRegion| is always valid.
-        // It can also be 0 if the flow has no region chain.
-        RenderRegion* m_containingRegion;
         LayoutUnit m_paginationStrut;
         LayoutUnit m_paginatedLineWidth;
         bool m_isFirstAfterPageBreak;