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

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 01825db216bfcbc45fe7b06d16d95043328839c5..62b15589bae3826beed1ee19ccbda28a4d87ceb3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -2709,6 +2709,14 @@ bool PaintLayer::paintsWithTransform(GlobalPaintFlags globalPaintFlags) const {
           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))