Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 8d1acb0fd921de3457807fea646a0663891ac439..76442a99e572512aadba33fc6382472f83b9adf6 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -322,7 +322,8 @@ void PaintLayer::dirtyAncestorChainHasSelfPaintingLayerDescendantStatus()
 
 bool PaintLayer::scrollsWithViewport() const
 {
-    return layoutObject()->style()->position() == FixedPosition && layoutObject()->containerForFixedPosition() == layoutObject()->view();
+    return (layoutObject()->style()->position() == FixedPosition && layoutObject()->containerForFixedPosition() == layoutObject()->view())
+        || (layoutObject()->style()->position() == StickyPosition && !ancestorScrollingLayer());
 }
 
 bool PaintLayer::scrollsWithRespectTo(const PaintLayer* other) const
@@ -720,7 +721,7 @@ bool PaintLayer::update3DTransformedDescendantStatus()
     return has3DTransform();
 }
 
-bool PaintLayer::updateLayerPosition()
+void PaintLayer::updateLayerPosition()
 {
     LayoutPoint localPoint;
     LayoutPoint inlineBoundingBoxOffset; // We don't put this into the Layer x/y for inlines, so we need to subtract it out when done.
@@ -771,10 +772,8 @@ bool PaintLayer::updateLayerPosition()
         localPoint -= scrollOffset;
     }
 
-    bool positionOrOffsetChanged = false;
     if (layoutObject()->isInFlowPositioned()) {
         LayoutSize newOffset = layoutObject()->offsetForInFlowPosition();
-        positionOrOffsetChanged = newOffset != m_offsetForInFlowPosition;
         m_offsetForInFlowPosition = newOffset;
         localPoint.move(m_offsetForInFlowPosition);
     } else {
@@ -785,7 +784,6 @@ bool PaintLayer::updateLayerPosition()
     localPoint.moveBy(-inlineBoundingBoxOffset);
 
     if (m_location != localPoint) {
-        positionOrOffsetChanged = true;
         setNeedsRepaint();
     }
     m_location = localPoint;
@@ -793,7 +791,6 @@ bool PaintLayer::updateLayerPosition()
 #if ENABLE(ASSERT)
     m_needsPositionUpdate = false;
 #endif
-    return positionOrOffsetChanged;
 }
 
 TransformationMatrix PaintLayer::perspectiveTransform() const