Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 44 matching lines @@
     BackgroundBleedClipLayer,
 };
 
 enum ContentChangeType {
     ImageChanged,
     CanvasChanged,
     CanvasContextChanged
 };
 
 class InlineFlowBox;
+class StickyPositionViewportConstraints;
 
 // This class is the base class for all CSS objects.
 //
 // All CSS objects follow the box model object. See THE BOX MODEL section in
 // LayoutBox for more information.
 //
 // This class actually doesn't have the box model but it exposes some common
 // functions or concepts that sub-classes can extend upon. For example, there
 // are accessors for margins, borders, paddings and borderBoundingBox().
 //
@@ skipping 58 matching lines @@
 public:
     LayoutBoxModelObject(ContainerNode*);
     ~LayoutBoxModelObject() override;
 
     // This is the only way layers should ever be destroyed.
     void destroyLayer();
 
     LayoutSize relativePositionOffset() const;
     LayoutSize relativePositionLogicalOffset() const { return style()->isHorizontalWritingMode() ? relativePositionOffset() : relativePositionOffset().transposedSize(); }
 
+    // Populates StickyPositionConstraints, setting the sticky box rect, containing block rect and updating
+    // the constraint offsets according to the available space.
+    void computeStickyPositionConstraints(StickyPositionViewportConstraints&, const LayoutRect& constrainingRect) const;
+    LayoutRect computeStickyConstrainingRect() const;
+    LayoutSize stickyPositionOffset() const;
+
     LayoutSize offsetForInFlowPosition() const;
 
     // IE extensions. Used to calculate offsetWidth/Height.  Overridden by inlines (LayoutFlow)
     // to return the remaining width on a given line (and the height of a single line).
     virtual LayoutUnit offsetLeft() const;
     virtual LayoutUnit offsetTop() const;
     virtual LayoutUnit offsetWidth() const = 0;
     virtual LayoutUnit offsetHeight() const = 0;
 
     int pixelSnappedOffsetLeft() const { return roundToInt(offsetLeft()); }
@@ skipping 212 matching lines @@
     // The PaintLayer associated with this object.
     // |m_layer| can be nullptr depending on the return value of layerTypeRequired().
     OwnPtr<PaintLayer> m_layer;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBoxModelObject, isBoxModelObject());
 
 } // namespace blink
 
 #endif // LayoutBoxModelObject_h