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

Source/core/layout/LayoutInline.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 124 matching lines @@
         LayoutObject* beforeChild, LayoutBoxModelObject* oldCont);
     void splitFlow(LayoutObject* beforeChild, LayoutBlock* newBlockBox,
         LayoutObject* newChild, LayoutBoxModelObject* oldCont);
 
     void layout() final { ASSERT_NOT_REACHED(); } // Do nothing for layout()
 
     void paint(const PaintInfo&, const LayoutPoint&) final;
 
     bool nodeAtPoint(HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) final;
 
-    DeprecatedPaintLayerType layerTypeRequired() const override { return isRelPositioned() || createsGroup() || hasClipPath() || style()->shouldCompositeForCurrentAnimations() || style()->hasCompositorProxy() ? NormalDeprecatedPaintLayer : NoDeprecatedPaintLayer; }
+    DeprecatedPaintLayerType layerTypeRequired() const override { return isInFlowPositioned() || createsGroup() || hasClipPath() || style()->shouldCompositeForCurrentAnimations() || style()->hasCompositorProxy() ? NormalDeprecatedPaintLayer : NoDeprecatedPaintLayer; }
 
     LayoutUnit offsetLeft() const final;
     LayoutUnit offsetTop() const final;
     LayoutUnit offsetWidth() const final { return linesBoundingBox().width(); }
     LayoutUnit offsetHeight() const final { return linesBoundingBox().height(); }
 
     LayoutRect absoluteClippedOverflowRect() const override;
     LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = nullptr) const override;
     LayoutRect rectWithOutlineForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, LayoutUnit outlineWidth, const PaintInvalidationState* = nullptr) const final;
     void mapRectToPaintInvalidationBacking(const LayoutBoxModelObject* paintInvalidationContainer, LayoutRect&, const PaintInvalidationState*) const final;
@@ skipping 35 matching lines @@
 
     LayoutObjectChildList m_children;
     LineBoxList m_lineBoxes; // All of the line boxes created for this inline flow.  For example, <i>Hello<br>world.</i> will have two <i> line boxes.
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutInline, isLayoutInline());
 
 } // namespace blink
 
 #endif // LayoutInline_h