Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 45 matching lines @@
 enum ResizerHitTestType {
     ResizerForPointer,
     ResizerForTouch
 };
 
 class PlatformEvent;
 class LayoutBox;
 class PaintLayer;
 class LayoutScrollbarPart;
 
+typedef WTF::HashMap<PaintLayer*, StickyPositionScrollingConstraints> StickyConstraintsMap;
+
+struct PaintLayerScrollableAreaRareData {
+    WTF_MAKE_NONCOPYABLE(PaintLayerScrollableAreaRareData);
+    USING_FAST_MALLOC(PaintLayerScrollableAreaRareData);
+public:
+    PaintLayerScrollableAreaRareData() {}
+
+    StickyConstraintsMap m_stickyConstraintsMap;
+};
+
 // PaintLayerScrollableArea represents the scrollable area of a LayoutBox.
 //
 // To be scrollable, an element requires ‘overflow’ != visible. Note that this
 // doesn’t imply having scrollbars as you can always programmatically scroll
 // when ‘overflow’ is hidden (using JavaScript's element.scrollTo or
 // scrollLeft).
 //
 // The size and scroll origin of the scrollable area are based on layout
 // dimensions. They are recomputed after layout in updateScrollDimensions.
 //
@@ skipping 254 matching lines @@
     const IntPoint& cachedOverlayScrollbarOffset() { return m_cachedOverlayScrollbarOffset; }
     void setCachedOverlayScrollbarOffset(const IntPoint& offset) { m_cachedOverlayScrollbarOffset = offset; }
 
     IntRect rectForHorizontalScrollbar(const IntRect& borderBoxRect) const;
     IntRect rectForVerticalScrollbar(const IntRect& borderBoxRect) const;
 
     Widget* widget() override;
     ScrollAnchor& scrollAnchor() { return m_scrollAnchor; }
     bool isPaintLayerScrollableArea() const override { return true; }
 
+    StickyConstraintsMap& stickyConstraintsMap() { return ensureRareData().m_stickyConstraintsMap; }
+    void invalidateStickyConstraints();
+
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit PaintLayerScrollableArea(PaintLayer&);
 
     bool hasHorizontalOverflow() const;
     bool hasVerticalOverflow() const;
     bool hasScrollableHorizontalOverflow() const;
     bool hasScrollableVerticalOverflow() const;
     bool visualViewportSuppliesScrollbars() const;
@@ skipping 16 matching lines @@
 
     // See comments on isPointInResizeControl.
     void updateResizerAreaSet();
     void updateResizerStyle();
 
 
     void updateScrollableAreaSet(bool hasOverflow);
 
     void updateCompositingLayersAfterScroll();
 
+    PaintLayerScrollableAreaRareData* rareData()
+    {
+        return m_rareData.get();
+    }
+
+    PaintLayerScrollableAreaRareData& ensureRareData()
+    {
+        if (!m_rareData)
+            m_rareData = adoptPtr(new PaintLayerScrollableAreaRareData());
+        return *m_rareData.get();
+    }
+
     // PaintInvalidationCapableScrollableArea
     LayoutBox& boxForScrollControlPaintInvalidation() const { return box(); }
 
     PaintLayer& m_layer;
 
     // Keeps track of whether the layer is currently resizing, so events can cause resizing to start and stop.
     unsigned m_inResizeMode : 1;
     unsigned m_scrollsOverflow : 1;
 
     unsigned m_inOverflowRelayout : 1;
@@ skipping 20 matching lines @@
     IntPoint m_cachedOverlayScrollbarOffset;
 
     // LayoutObject to hold our custom scroll corner.
     LayoutScrollbarPart* m_scrollCorner;
 
     // LayoutObject to hold our custom resizer.
     LayoutScrollbarPart* m_resizer;
 
     ScrollAnchor m_scrollAnchor;
 
+    OwnPtr<PaintLayerScrollableAreaRareData> m_rareData;
+
 #if ENABLE(ASSERT)
     bool m_hasBeenDisposed;
 #endif
 };
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea, ScrollableArea, scrollableArea,
     scrollableArea->isPaintLayerScrollableArea(),
     scrollableArea.isPaintLayerScrollableArea());
 
 } // namespace blink
 
 #endif // LayerScrollableArea_h