Adapt and reland old position sticky implementation

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.h
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.h b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.h
index d182c9263b12a5ea432cbcbef241ec3f10c42d20..1ebe886bcca7a12820239c09cbc6668c0be42227 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.h
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.h
@@ -31,9 +31,10 @@ private:
     };
 
     struct AncestorInfo {
-        AncestorInfo()
+        explicit AncestorInfo(PaintLayer* rootLayer)

[chrishtr, 2016/03/09 16:53:08]

You should be able to initialize lastOverflowLayer inside of updateRecursive,
similarly to how it works for ancestorStackingContext

[flackr, 2016/03/14 19:04:26]

Done.

             : ancestorStackingContext(nullptr)
             , enclosingCompositedLayer(nullptr)
+            , lastOverflowLayer(rootLayer)
             , lastScrollingAncestor(nullptr)
             , hasAncestorWithClipRelatedProperty(false)
             , hasAncestorWithClipPath(false)
@@ -42,6 +43,7 @@ private:
 
         PaintLayer* ancestorStackingContext;
         PaintLayer* enclosingCompositedLayer;
+        PaintLayer* lastOverflowLayer;
         // 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