Adapt and reland old position sticky implementation

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 13d47ed65312bccaf58d87b8794b631698091fa5..c494e389db082674b587848e572b198824621fe4 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1232,6 +1232,23 @@ void PaintLayerScrollableArea::updateResizerStyle()
     }
 }
 
+void PaintLayerScrollableArea::invalidateStickyConstraints()
+{
+    if (PaintLayerScrollableAreaRareData* d = rareData()) {
+        for (PaintLayer* stickyLayer : d->m_stickyConstraintsMap.keys()) {
+            stickyLayer->setNeedsCompositingInputsUpdate();
+        }
+        d->m_stickyConstraintsMap.clear();
+    }
+}
+
+void PaintLayerScrollableArea::invalidateStickyConstraintsFor(PaintLayer* layer)
+{
+    if (PaintLayerScrollableAreaRareData* d = rareData()) {
+        d->m_stickyConstraintsMap.remove(layer);
+    }
+}
+
 IntSize PaintLayerScrollableArea::offsetFromResizeCorner(const IntPoint& absolutePoint) const
 {
     // Currently the resize corner is either the bottom right corner or the bottom left corner.