Only automatically promote sticky position elements which move with scroll.

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index a6285cff3901fcd8435a86417ca01594799a0238..038b18ea6026315244ab4963d577fdde4cf4d2e0 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -621,7 +621,13 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
 
   bool isInTopLayer() const;
 
-  bool sticksToViewport() const;
+  // Returns true if the layer is sticky position and may stick to its
+  // ancestor overflow layer.
+  bool sticksToScroller() const;
+
+  // Returns true if the layer is fixed position and will not move with
+  // scrolling.
+  bool fixedToViewport() const;
   bool scrollsWithRespectTo(const PaintLayer*) const;
 
   void addLayerHitTestRects(LayerHitTestRects&) const;