Adapt and reland old position sticky implementation

Source/core/layout/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/layout/compositing/CompositingReasonFinder.h"
 
 #include "core/CSSPropertyNames.h"
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
@@ skipping 145 matching lines @@
     // scrolling layer is not not on the stacking context ancestor chain of |layer|.
     // See the definition of the scrollParent property in Layer for more detail.
     if (const DeprecatedPaintLayer* scrollingAncestor = layer->ancestorScrollingLayer()) {
         if (scrollingAncestor->needsCompositedScrolling() && layer->scrollParent())
             directReasons |= CompositingReasonOverflowScrollingParent;
     }
 
     if (requiresCompositingForPositionFixed(layer))
         directReasons |= CompositingReasonPositionFixed;
 
+    if (layer->scrollsWithScrollAncestor())
+        directReasons |= CompositingReasonPositionSticky;
+
     directReasons |= layoutObject->additionalCompositingReasons();
 
     ASSERT(!(directReasons & CompositingReasonComboAllStyleDeterminedReasons));
     return directReasons;
 }
 
 bool CompositingReasonFinder::requiresCompositingForAnimation(const ComputedStyle& style) const
 {
     if (style.subtreeWillChangeContents())
         return style.isRunningAnimationOnCompositor();
 
     return style.shouldCompositeForCurrentAnimations();
 }
 
 bool CompositingReasonFinder::requiresCompositingForPositionFixed(const DeprecatedPaintLayer* layer) const
 {
     if (!(m_compositingTriggers & ViewportConstrainedPositionedTrigger))
         return false;
     // Don't promote fixed position elements that are descendants of a non-view container, e.g. transformed elements.
     // They will stay fixed wrt the container rather than the enclosing frame.
     return layer->scrollsWithViewport() && m_layoutView.frameView()->isScrollable();
 }
 
 }