Do not promote position sticky or fixed elements unless they move with scroll.

third_party/WebKit/Source/core/style/ComputedStyle.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 3176 matching lines @@
   // Position utility functions.
   bool hasOutOfFlowPosition() const {
     return position() == EPosition::kAbsolute ||
            position() == EPosition::kFixed;
   }
   bool hasInFlowPosition() const {
     return position() == EPosition::kRelative ||
            position() == EPosition::kSticky;
   }
   bool hasViewportConstrainedPosition() const {
-    return position() == EPosition::kFixed || position() == EPosition::kSticky;
+    return position() == EPosition::kFixed;
+  }
+  bool hasStickyConstrainedPosition() const {
+    return position() == EPosition::kSticky &&
+           (!top().isAuto() || !left().isAuto() || !right().isAuto() ||
+            !bottom().isAuto());
   }
 
   // Clip utility functions.
   const Length& clipLeft() const { return m_visual->clip.left(); }
   const Length& clipRight() const { return m_visual->clip.right(); }
   const Length& clipTop() const { return m_visual->clip.top(); }
   const Length& clipBottom() const { return m_visual->clip.bottom(); }
 
   // Offset utility functions.
   // Accessors for positioned object edges that take into account writing mode.
@@ skipping 641 matching lines @@
   m_nonInheritedData.m_pseudoBits |= 1 << (pseudo - 1);
 }
 
 inline bool ComputedStyle::hasPseudoElementStyle() const {
   return m_nonInheritedData.m_pseudoBits & ElementPseudoIdMask;
 }
 
 }  // namespace blink
 
 #endif  // ComputedStyle_h