Handle nested position:sticky elements correctly (compositor)

third_party/WebKit/Source/core/layout/compositing/CompositingReasonFinder.cpp

 // 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.
 
 #include "core/layout/compositing/CompositingReasonFinder.h"
 
 #include "core/CSSPropertyNames.h"
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
@@ skipping 214 matching lines @@
            LayoutRect(layer->boundingBoxForCompositing())) ||
        layer->compositesWithTransform() || layer->compositesWithOpacity())) {
     return false;
   }
   // Don't promote fixed position elements that are descendants of a non-view
   // container, e.g. transformed elements.  They will stay fixed wrt the
   // container rather than the enclosing frame.
   if (layer->sticksToViewport())
     return m_layoutView.frameView()->isScrollable();
 
-  if (layer->layoutObject().style()->position() != EPosition::kSticky)
-    return false;
-
-  // Don't promote nested sticky elements; the compositor can't handle them.
-  // TODO(smcgruer): Add cc nested sticky support (http://crbug.com/672710)
-  PaintLayerScrollableArea* scrollableArea =
-      layer->ancestorOverflowLayer()->getScrollableArea();
-  DCHECK(scrollableArea->stickyConstraintsMap().contains(
-      const_cast<PaintLayer*>(layer)));
-
-  return layer->ancestorOverflowLayer()->scrollsOverflow() &&
-         !scrollableArea->stickyConstraintsMap()
-              .at(const_cast<PaintLayer*>(layer))
-              .hasAncestorStickyElement();
+  return layer->layoutObject().style()->position() == EPosition::kSticky &&
+         layer->ancestorOverflowLayer()->scrollsOverflow();
 }
 
 }  // namespace blink