Reland main thread position sticky implementation.

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 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@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1217 matching lines @@
             m_resizer = LayoutScrollbarPart::createAnonymous(&box().document(), this);
             m_resizer->setDangerousOneWayParent(&box());
         }
         m_resizer->setStyleWithWritingModeOfParent(resizer.release());
     } else if (m_resizer) {
         m_resizer->destroy();
         m_resizer = nullptr;
     }
 }
 
+void PaintLayerScrollableArea::invalidateAllStickyConstraints()
+{
+    if (PaintLayerScrollableAreaRareData* d = rareData()) {
+        for (PaintLayer* stickyLayer : d->m_stickyConstraintsMap.keys()) {
+            if (stickyLayer->layoutObject()->style()->position() == StickyPosition)
+                stickyLayer->setNeedsCompositingInputsUpdate();
+        }
+        d->m_stickyConstraintsMap.clear();
+    }
+}
+
+void PaintLayerScrollableArea::invalidateStickyConstraintsFor(PaintLayer* layer, bool needsCompositingUpdate)
+{
+    if (PaintLayerScrollableAreaRareData* d = rareData()) {
+        d->m_stickyConstraintsMap.remove(layer);
+        if (needsCompositingUpdate && layer->layoutObject()->style()->position() == StickyPosition)
+            layer->setNeedsCompositingInputsUpdate();
+    }
+}
+
 IntSize PaintLayerScrollableArea::offsetFromResizeCorner(const IntPoint& absolutePoint) const
 {
     // Currently the resize corner is either the bottom right corner or the bottom left corner.
     // FIXME: This assumes the location is 0, 0. Is this guaranteed to always be the case?
     IntSize elementSize = layer()->size();
     if (box().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
         elementSize.setWidth(0);
     IntPoint resizerPoint = IntPoint(elementSize);
     IntPoint localPoint = roundedIntPoint(box().absoluteToLocal(absolutePoint, UseTransforms));
     return localPoint - resizerPoint;
@@ skipping 338 matching lines @@
 }
 
 DEFINE_TRACE(PaintLayerScrollableArea::ScrollbarManager)
 {
     visitor->trace(m_scrollableArea);
     visitor->trace(m_hBar);
     visitor->trace(m_vBar);
 }
 
 } // namespace blink