Adapt and reland old position sticky implementation

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 3932a006ce92e9f3f11a1ed8cce432930cf27b5b..2c01e6ec1bcc01f4134321ced4b1ed2631ecd466 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -264,6 +264,8 @@ public:
     // Allows updates of layer content without invalidating paint.
     void contentChanged(ContentChangeType);
 
+    void updateLayerPosition();
+
     void updateLayerPositionsAfterLayout();
     void updateLayerPositionsAfterOverflowScroll(const DoubleSize& scrollDelta);
 
@@ -527,17 +529,25 @@ public:
             : opacityAncestor(nullptr)
             , transformAncestor(nullptr)
             , filterAncestor(nullptr)
+            , ancestorOverflowLayer(nullptr)
             , ancestorScrollingLayer(nullptr)
             , nearestFixedPositionLayer(nullptr)
             , scrollParent(nullptr)
             , clipParent(nullptr)
         { }
 
-        bool isDefault() const { return !opacityAncestor && !transformAncestor && !filterAncestor && !ancestorScrollingLayer && !nearestFixedPositionLayer && !scrollParent && !clipParent; }
+        bool isDefault() const { return !opacityAncestor && !transformAncestor && !filterAncestor && !ancestorOverflowLayer && !ancestorScrollingLayer && !nearestFixedPositionLayer && !scrollParent && !clipParent; }
 
         const PaintLayer* opacityAncestor;
         const PaintLayer* transformAncestor;
         const PaintLayer* filterAncestor;
+
+        // The first ancestor having a non visible overflow.
+        const PaintLayer* ancestorOverflowLayer;
+
+        // The fist ancestor which can scroll. This is a subset of the
+        // ancestorOverflowLayer chain where the scrolling layer is visible and
+        // has a larger scroll content than its bounds.
         const PaintLayer* ancestorScrollingLayer;
         const PaintLayer* nearestFixedPositionLayer;
 
@@ -576,6 +586,7 @@ public:
     const PaintLayer* transformAncestor() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_rareAncestorDependentCompositingInputs ? m_rareAncestorDependentCompositingInputs->transformAncestor : nullptr; }
     const PaintLayer* filterAncestor() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_rareAncestorDependentCompositingInputs ? m_rareAncestorDependentCompositingInputs->filterAncestor : nullptr; }
     const LayoutObject* clippingContainer() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_ancestorDependentCompositingInputs.clippingContainer; }
+    const PaintLayer* ancestorOverflowLayer() const { return m_rareAncestorDependentCompositingInputs ? m_rareAncestorDependentCompositingInputs->ancestorOverflowLayer : nullptr; }
     const PaintLayer* ancestorScrollingLayer() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_rareAncestorDependentCompositingInputs ? m_rareAncestorDependentCompositingInputs->ancestorScrollingLayer : nullptr; }
     const PaintLayer* nearestFixedPositionLayer() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_rareAncestorDependentCompositingInputs ? m_rareAncestorDependentCompositingInputs->nearestFixedPositionLayer : nullptr; }
     const PaintLayer* scrollParent() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_rareAncestorDependentCompositingInputs ? m_rareAncestorDependentCompositingInputs->scrollParent : nullptr; }
@@ -687,9 +698,6 @@ private:
 
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
-    // Returns true if the position changed.
-    bool updateLayerPosition();
-
     void updateLayerPositionRecursive();
     void updateLayerPositionsAfterScrollRecursive(const DoubleSize& scrollDelta, bool paintInvalidationContainerWasScrolled);