Only automatically promote sticky position elements which move with scroll.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 4992 matching lines @@
 
   for (const LayoutObject* layoutObject : *viewportConstrainedObjects()) {
     DCHECK(layoutObject->isBoxModelObject() && layoutObject->hasLayer());
     DCHECK(layoutObject->style()->position() == EPosition::kFixed ||
            layoutObject->style()->position() == EPosition::kSticky);
     PaintLayer* layer = toLayoutBoxModelObject(layoutObject)->layer();
 
     // Whether the Layer sticks to the viewport is a tree-depenent
     // property and our viewportConstrainedObjects collection is maintained
     // with only LayoutObject-level information.
-    if (!layer->sticksToViewport())
+    if (!layer->fixedToViewport() && !layer->sticksToScroller())
       continue;
 
     // If the whole subtree is invisible, there's no reason to scroll on
     // the main thread because we don't need to generate invalidations
     // for invisible content.
     if (layer->subtreeIsInvisible())
       continue;
 
     // We're only smart enough to scroll viewport-constrainted objects
     // in the compositor if they have their own backing or they paint
@@ skipping 227 matching lines @@
 void FrameView::setAnimationHost(
     std::unique_ptr<CompositorAnimationHost> host) {
   m_animationHost = std::move(host);
 }
 
 LayoutUnit FrameView::caretWidth() const {
   return LayoutUnit(getHostWindow()->windowToViewportScalar(1));
 }
 
 }  // namespace blink