Only promote fixed position elements on low dpi without transform or opacity.

third_party/WebKit/Source/core/paint/PaintLayer.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@web.de>
@@ skipping 2691 matching lines @@
          m_rareData->compositedLayerMapping->hasChildClippingMaskLayer();
 }
 
 bool PaintLayer::paintsWithTransform(GlobalPaintFlags globalPaintFlags) const {
   return (transform() ||
           layoutObject()->style()->position() == FixedPosition) &&
          ((globalPaintFlags & GlobalPaintFlattenCompositingLayers) ||
           compositingState() != PaintsIntoOwnBacking);
 }
 
+bool PaintLayer::compositesWithTransform() const {
+  return transformAncestor() || transform();
+}
+
+bool PaintLayer::compositesWithOpacity() const {
+  return opacityAncestor() || layoutObject()->style()->hasOpacity();
+}
+
 bool PaintLayer::backgroundIsKnownToBeOpaqueInRect(
     const LayoutRect& localRect) const {
   if (paintsWithTransparency(GlobalPaintNormalPhase))
     return false;
 
   // We can't use hasVisibleContent(), because that will be true if our
   // layoutObject is hidden, but some child is visible and that child doesn't
   // cover the entire rect.
   if (layoutObject()->style()->visibility() != EVisibility::Visible)
     return false;
@@ skipping 544 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif