Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.h

 // 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.
 
 #ifndef CompositingInputsUpdater_h
 #define CompositingInputsUpdater_h
 
 #include "core/layout/LayoutGeometryMap.h"
 #include "wtf/Allocator.h"
 
@@ skipping 16 matching lines @@
 private:
     enum UpdateType {
         DoNotForceUpdate,
         ForceUpdate,
     };
 
     struct AncestorInfo {
         AncestorInfo()
             : ancestorStackingContext(nullptr)
             , enclosingCompositedLayer(nullptr)
+            , lastOverflowLayer(nullptr)
             , lastScrollingAncestor(nullptr)
             , hasAncestorWithClipRelatedProperty(false)
             , hasAncestorWithClipPath(false)
         {
         }
 
         PaintLayer* ancestorStackingContext;
         PaintLayer* enclosingCompositedLayer;
+        PaintLayer* lastOverflowLayer;

[chrishtr, 2016/03/24 17:36:03]

lastOverflowClipLayer

[flackr, 2016/03/29 16:02:32]

Done.

         // Notice that lastScrollingAncestor isn't the same thing as
         // ancestorScrollingLayer. The former is just the nearest scrolling
         // along the PaintLayer::parent() chain. The latter is the layer that
         // actually controls the scrolling of this layer, which we find on the
         // containing block chain.
         PaintLayer* lastScrollingAncestor;
         bool hasAncestorWithClipRelatedProperty;
         bool hasAncestorWithClipPath;
     };
 
     void updateRecursive(PaintLayer*, UpdateType, AncestorInfo);
 
     LayoutGeometryMap m_geometryMap;
     PaintLayer* m_rootLayer;
 };
 
 } // namespace blink
 
 #endif // CompositingInputsUpdater_h