*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/rendering/RenderObject.h

Index: Source/core/rendering/RenderObject.h
diff --git a/Source/core/rendering/RenderObject.h b/Source/core/rendering/RenderObject.h
index 492dd4f1a3b4ebd4c07466b74edc9c5f1f733358..57e23f48ae8b9db625e458b0c5b678ff4801ce8a 100644
--- a/Source/core/rendering/RenderObject.h
+++ b/Source/core/rendering/RenderObject.h
@@ -57,11 +57,9 @@ class PseudoStyleRequest;
 class RenderBoxModelObject;
 class RenderInline;
 class RenderBlock;
-class RenderFlowThread;
 class RenderGeometryMap;
 class RenderLayer;
 class RenderLayerModelObject;
-class RenderNamedFlowThread;
 class RenderSVGResourceContainer;
 class RenderTable;
 class RenderTheme;
@@ -203,17 +201,6 @@ public:
 
     RenderBox* enclosingScrollableBox() const;
 
-    // Function to return our enclosing flow thread if we are contained inside one. This
-    // function follows the containing block chain.
-    RenderFlowThread* flowThreadContainingBlock() const
-    {
-        if (flowThreadState() == NotInsideFlowThread)
-            return 0;
-        return locateFlowThreadContainingBlock();
-    }
-
-    RenderNamedFlowThread* renderNamedFlowThreadWrapper() const;
-
     virtual bool isEmpty() const { return firstChild() == 0; }
 
 #ifndef NDEBUG
@@ -273,13 +260,6 @@ protected:
     void setParent(RenderObject* parent)
     {
         m_parent = parent;
-
-        // Only update if our flow thread state is different from our new parent and if we're not a RenderFlowThread.
-        // A RenderFlowThread is always considered to be inside itself, so it never has to change its state
-        // in response to parent changes.
-        FlowThreadState newState = parent ? parent->flowThreadState() : NotInsideFlowThread;
-        if (newState != flowThreadState() && !isRenderFlowThread())
-            setFlowThreadStateIncludingDescendants(newState);
     }
 
     //////////////////////////////////////////
@@ -345,8 +325,6 @@ public:
     virtual bool isRenderImage() const { return false; }
     virtual bool isRenderInline() const { return false; }
     virtual bool isRenderPart() const { return false; }
-    virtual bool isRenderRegion() const { return false; }
-    virtual bool isRenderNamedFlowFragment() const { return false; }
     virtual bool isRenderView() const { return false; }
     virtual bool isReplica() const { return false; }
 
@@ -374,15 +352,6 @@ public:
 
     virtual bool isRenderGrid() const { return false; }
 
-    virtual bool isRenderFlowThread() const { return false; }
-    virtual bool isRenderNamedFlowThread() const { return false; }
-    bool isInFlowRenderFlowThread() const { return isRenderFlowThread() && !isOutOfFlowPositioned(); }
-    bool isOutOfFlowRenderFlowThread() const { return isRenderFlowThread() && isOutOfFlowPositioned(); }
-    bool isRenderNamedFlowFragmentContainer() const;
-
-    virtual bool isRenderMultiColumnBlock() const { return false; }
-    virtual bool isRenderMultiColumnSet() const { return false; }
-
     virtual bool isRenderScrollbarPart() const { return false; }
 
     bool isRoot() const { return document().documentElement() == m_node; }
@@ -414,17 +383,6 @@ public:
             setNeedsLayout();
     }
 
-    enum FlowThreadState {
-        NotInsideFlowThread = 0,
-        InsideOutOfFlowThread = 1,
-        InsideInFlowThread = 2,
-    };
-
-    void setFlowThreadStateIncludingDescendants(FlowThreadState);
-
-    FlowThreadState flowThreadState() const { return m_bitfields.flowThreadState(); }
-    void setFlowThreadState(FlowThreadState state) { m_bitfields.setFlowThreadState(state); }
-
     // FIXME: Until all SVG renders can be subclasses of RenderSVGModelObject we have
     // to add SVG renderer methods to RenderObject with an ASSERT_NOT_REACHED() default implementation.
     virtual bool isSVG() const { return false; }
@@ -492,7 +450,7 @@ public:
         // RenderBlock::createAnonymousBlock(). This includes creating an anonymous
         // RenderBlock having a BLOCK or BOX display. Other classes such as RenderTextFragment
         // are not RenderBlocks and will return false. See https://bugs.webkit.org/show_bug.cgi?id=56709.
-        return isAnonymous() && (style()->display() == BLOCK || style()->display() == BOX) && style()->styleType() == NOPSEUDO && isRenderBlock() && !isListMarker() && !isRenderFlowThread()
+        return isAnonymous() && (style()->display() == BLOCK || style()->display() == BOX) && style()->styleType() == NOPSEUDO && isRenderBlock() && !isListMarker()
             && !isRenderFullScreen()
             && !isRenderFullScreenPlaceholder();
     }
@@ -720,7 +678,7 @@ public:
 
     bool canContainFixedPositionObjects() const
     {
-        return isRenderView() || (hasTransform() && isRenderBlock()) || isSVGForeignObject() || isOutOfFlowRenderFlowThread();
+        return isRenderView() || (hasTransform() && isRenderBlock()) || isSVGForeignObject();
     }
     bool canContainAbsolutePositionObjects() const
     {
@@ -1049,10 +1007,6 @@ protected:
 private:
     RenderBlock* containerForFixedPosition(const RenderLayerModelObject* repaintContainer = 0, bool* repaintContainerSkipped = 0) const;
 
-    RenderFlowThread* locateFlowThreadContainingBlock() const;
-    void removeFromRenderFlowThread();
-    void removeFromRenderFlowThreadRecursive(RenderFlowThread*);
-
     bool shouldRepaintForStyleDifference(StyleDifference) const;
     bool hasImmediateNonWhitespaceTextChildOrPropertiesDependentOnColor() const;
 
@@ -1130,7 +1084,6 @@ private:
             , m_layoutDidGetCalled(false)
             , m_positionedState(IsStaticallyPositioned)
             , m_selectionState(SelectionNone)
-            , m_flowThreadState(NotInsideFlowThread)
             , m_boxDecorationState(NoBoxDecorations)
         {
         }
@@ -1172,7 +1125,6 @@ private:
     private:
         unsigned m_positionedState : 2; // PositionedState
         unsigned m_selectionState : 3; // SelectionState
-        unsigned m_flowThreadState : 2; // FlowThreadState
         unsigned m_boxDecorationState : 2; // BoxDecorationState
 
     public:
@@ -1191,9 +1143,6 @@ private:
         ALWAYS_INLINE SelectionState selectionState() const { return static_cast<SelectionState>(m_selectionState); }
         ALWAYS_INLINE void setSelectionState(SelectionState selectionState) { m_selectionState = selectionState; }
 
-        ALWAYS_INLINE FlowThreadState flowThreadState() const { return static_cast<FlowThreadState>(m_flowThreadState); }
-        ALWAYS_INLINE void setFlowThreadState(FlowThreadState flowThreadState) { m_flowThreadState = flowThreadState; }
-
         ALWAYS_INLINE BoxDecorationState boxDecorationState() const { return static_cast<BoxDecorationState>(m_boxDecorationState); }
         ALWAYS_INLINE void setBoxDecorationState(BoxDecorationState boxDecorationState) { m_boxDecorationState = boxDecorationState; }
     };