Clean compositing inputs for location APIs for sticky-affected elements.

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 128 matching lines @@
     return;
 
   Layer()->ContentChanged(change_type);
 }
 
 bool LayoutBoxModelObject::HasAcceleratedCompositing() const {
   return View()->Compositor()->HasAcceleratedCompositing();
 }
 
 LayoutBoxModelObject::LayoutBoxModelObject(ContainerNode* node)
-    : LayoutObject(node) {}
+    : LayoutObject(node), is_in_sticky_subtree_(false) {}
 
 bool LayoutBoxModelObject::UsesCompositedScrolling() const {
   return HasOverflowClip() && HasLayer() &&
          Layer()->GetScrollableArea()->UsesCompositedScrolling();
 }
 
 BackgroundPaintLocation LayoutBoxModelObject::GetBackgroundPaintLocation(
     uint32_t* reasons) const {
   bool has_custom_scrollbars = false;
   // TODO(flackr): Detect opaque custom scrollbars which would cover up a
@@ skipping 310 matching lines @@
         // scroll reasons are recomputed.
       }
     }
 
     if (new_style_is_viewport_constained != old_style_is_viewport_constrained) {
       if (new_style_is_viewport_constained && Layer())
         frame_view->AddViewportConstrainedObject(*this);
       else
         frame_view->RemoveViewportConstrainedObject(*this);
     }
+
+    is_in_sticky_subtree_ =
+        new_style_is_sticky ||
+        (Parent() && Parent()->EnclosingBoxModelObject() &&

[chrishtr, 2017/04/20 17:40:34]

Shouldn't this use the containing block chain, not the parent chain?

[smcgruer, 2017/04/26 14:37:07]

No longer relevant; see new PS.

+         Parent()->EnclosingBoxModelObject()->IsInStickySubtree());
   }
 }
 
 void LayoutBoxModelObject::InvalidateStickyConstraints() {
   PaintLayer* enclosing = EnclosingLayer();
 
   if (PaintLayerScrollableArea* scrollable_area =
           enclosing->GetScrollableArea()) {
     scrollable_area->InvalidateAllStickyConstraints();
     // If this object doesn't have a layer and its enclosing layer is a scroller
@@ skipping 991 matching lines @@
   if (root_element_style->HasBackground())
     return false;
 
   if (GetNode() != GetDocument().FirstBodyElement())
     return false;
 
   return true;
 }
 
 }  // namespace blink