Adapt and reland old position sticky implementation

Source/core/paint/DeprecatedPaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 295 matching lines @@
         // in this case, there is no need to dirty our ancestors further.
         if (layer->isSelfPaintingLayer()) {
             ASSERT(!parent() || parent()->m_hasSelfPaintingLayerDescendantDirty || parent()->m_hasSelfPaintingLayerDescendant);
             break;
         }
     }
 }
 
 bool DeprecatedPaintLayer::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 DeprecatedPaintLayer::scrollsWithScrollAncestor() const
+{
+    // TODO(flackr): This could check if the ancestor scroller for this layer is scrollable and
+    // composited but this would need to be determined before the composite phase as it's used
+    // as a compositing reason.

[flackr, 2015/09/15 21:13:11]

Is there an easy way to check the scroll ancestor before the ancestor depending
compositing inputs?

+    return layoutObject()->style()->position() == StickyPosition;
 }
 
 bool DeprecatedPaintLayer::scrollsWithRespectTo(const DeprecatedPaintLayer* other) const
 {
     if (scrollsWithViewport() != other->scrollsWithViewport())
         return true;
     return ancestorScrollingLayer() != other->ancestorScrollingLayer();
 }
 
 void DeprecatedPaintLayer::updateLayerPositionsAfterOverflowScroll(const DoubleSize& scrollDelta)
@@ skipping 2415 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif