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

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 6ad2d20bb56da59d9cafc49d91fa7e5d016a897c..03af306c6bc464e8dfd4a7299403e57310e970aa 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -559,6 +559,12 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
             compositingState() != PaintsIntoOwnBacking);
   }
 
+  // Returns true if the element or any ancestor is transformed.
+  bool compositesWithTransform() const;
+
+  // Returns true if the element or any ancestor has non 1 opacity.
+  bool compositesWithOpacity() const;
+
   bool paintsWithTransform(GlobalPaintFlags) const;
 
   // Returns true if background phase is painted opaque in the given rect.