Add position: sticky as supported position value when CSSStickyPosition is enabled.

Source/core/layout/LayoutObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 488 matching lines @@
             && !isLayoutFullScreen()
             && !isLayoutFullScreenPlaceholder();
     }
     bool isElementContinuation() const { return node() && node()->layoutObject() != this; }
     bool isInlineElementContinuation() const { return isElementContinuation() && isInline(); }
     virtual LayoutBoxModelObject* virtualContinuation() const { return nullptr; }
 
     bool isFloating() const { return m_bitfields.floating(); }
 
     bool isOutOfFlowPositioned() const { return m_bitfields.isOutOfFlowPositioned(); } // absolute or fixed positioning
+    bool isInFlowPositioned() const { return m_bitfields.isInFlowPositioned(); } // relative or sticky positioning
     bool isRelPositioned() const { return m_bitfields.isRelPositioned(); } // relative positioning
+    bool isStickyPositioned() const { return m_bitfields.isStickyPositioned(); } // sticky positioning
     bool isPositioned() const { return m_bitfields.isPositioned(); }
 
     bool isText() const  { return m_bitfields.isText(); }
     bool isBox() const { return m_bitfields.isBox(); }
     bool isInline() const { return m_bitfields.isInline(); } // inline object
     bool isDragging() const { return m_bitfields.isDragging(); }
     bool isReplaced() const { return m_bitfields.isReplaced(); } // a "replaced" element (see CSS)
     bool isHorizontalWritingMode() const { return m_bitfields.horizontalWritingMode(); }
     bool hasFlippedBlocksWritingMode() const
     {
@@ skipping 752 matching lines @@
         unsigned m_##name : 1;\
     public:\
         bool name() const { return m_##name; }\
         void set##Name(bool name) { m_##name = name; }\
 
     class LayoutObjectBitfields {
         enum PositionedState {
             IsStaticallyPositioned = 0,
             IsRelativelyPositioned = 1,
             IsOutOfFlowPositioned = 2,
+            IsStickyPositioned = 3,
         };
 
     public:
         LayoutObjectBitfields(Node* node)
             : m_selfNeedsLayout(false)
             , m_shouldInvalidateOverflowForPaint(false)
             // FIXME: We should remove mayNeedPaintInvalidation once we are able to
             // use the other layout flags to detect the same cases. crbug.com/370118
             , m_mayNeedPaintInvalidation(false)
             , m_shouldInvalidateSelection(false)
@@ skipping 89 matching lines @@
 
     private:
         unsigned m_positionedState : 2; // PositionedState
         unsigned m_selectionState : 3; // SelectionState
         unsigned m_boxDecorationBackgroundState : 2; // BoxDecorationBackgroundState
         unsigned m_fullPaintInvalidationReason : 5; // PaintInvalidationReason
 
     public:
         bool isOutOfFlowPositioned() const { return m_positionedState == IsOutOfFlowPositioned; }
         bool isRelPositioned() const { return m_positionedState == IsRelativelyPositioned; }
+        bool isStickyPositioned() const { return m_positionedState == IsStickyPositioned; }
+        bool isInFlowPositioned() const { return m_positionedState == IsRelativelyPositioned || m_positionedState == IsStickyPositioned; }
         bool isPositioned() const { return m_positionedState != IsStaticallyPositioned; }
 
         void setPositionedState(int positionState)
         {
             // This mask maps FixedPosition and AbsolutePosition to IsOutOfFlowPositioned, saving one bit.
             m_positionedState = static_cast<PositionedState>(positionState & 0x3);
         }
         void clearPositionedState() { m_positionedState = StaticPosition; }
 
         ALWAYS_INLINE SelectionState selectionState() const { return static_cast<SelectionState>(m_selectionState); }
@@ skipping 256 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h