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

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

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
index 562f5bb5d925ff0cf8a10835865133e3378b361a..2b4c6b5186c5d55ae2fa42585edcd96e356d3243 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
@@ -146,7 +146,7 @@ bool LayoutBoxModelObject::HasAcceleratedCompositing() const {
 }
 
 LayoutBoxModelObject::LayoutBoxModelObject(ContainerNode* node)
-    : LayoutObject(node) {}
+    : LayoutObject(node), is_in_sticky_subtree_(false) {}
 
 bool LayoutBoxModelObject::UsesCompositedScrolling() const {
   return HasOverflowClip() && HasLayer() &&
@@ -477,6 +477,11 @@ void LayoutBoxModelObject::StyleDidChange(StyleDifference diff,
       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());
   }
 }