Only automatically promote sticky position elements which move with scroll.

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 229 matching lines @@
     OverlapMap& overlapMap,
     RecursionData& currentRecursionData,
     bool& descendantHas3DTransform,
     Vector<PaintLayer*>& unclippedDescendants,
     IntRect& absoluteDescendantBoundingBox) {
   PaintLayerCompositor* compositor = m_layoutView.compositor();
 
   layer->stackingNode()->updateLayerListsIfNeeded();
 
   CompositingReasons reasonsToComposite = CompositingReasonNone;
-  CompositingReasons directReasons =
-      m_compositingReasonFinder.directReasons(layer);
+  CompositingReasons directReasons = CompositingReasonNone;
 
   // Video is special. It's the only PaintLayer type that can both have
   // PaintLayer children and whose children can't use its backing to render
   // into. These children (the controls) always need to be promoted into their
   // own layers to draw on top of the accelerated video.
   if (currentRecursionData.m_compositingAncestor &&
       currentRecursionData.m_compositingAncestor->layoutObject().isVideo())
     directReasons |= CompositingReasonVideoOverlay;
 
   bool hasCompositedScrollingAncestor =
       layer->ancestorScrollingLayer() &&
-      (m_compositingReasonFinder.directReasons(
-           layer->ancestorScrollingLayer()) &
+      (m_compositingReasonFinder.directReasons(layer->ancestorScrollingLayer(),
+                                               false) &
        CompositingReasonOverflowScrollingTouch);
 
   // TODO(chrishtr): use |hasCompositedScrollingAncestor| instead.
-  if (currentRecursionData.m_hasCompositedScrollingAncestor &&
-      layer->layoutObject().styleRef().hasViewportConstrainedPosition())
-    directReasons |= CompositingReasonScrollDependentPosition;
+  const bool ignoreLCDText =
+      currentRecursionData.m_hasCompositedScrollingAncestor;
+  directReasons |=
+      m_compositingReasonFinder.directReasons(layer, ignoreLCDText);
 
   bool canBeComposited = compositor->canBeComposited(layer);
   if (canBeComposited) {
     reasonsToComposite |= directReasons;
 
     if (layer->isRootLayer() && compositor->rootShouldAlwaysComposite())
       reasonsToComposite |= CompositingReasonRoot;
 
     // Add CompositingReasonOverflowScrollingTouch for layers that do not
     // already have it but need it.
@@ skipping 257 matching lines @@
     descendantHas3DTransform |=
         anyDescendantHas3DTransform || layer->has3DTransform();
   }
 
   // At this point we have finished collecting all reasons to composite this
   // layer.
   layer->setCompositingReasons(reasonsToComposite);
 }
 
 }  // namespace blink