blink: minor cleanup for overflow: clip

Renames variable in LayoutBoxModelObject::ComputeStickyConstrainingRect
to indicate it's a scroll-container.
Changes CompositingInputsUpdater to look for scroll-container.

BUG=1087667

Change-Id: If75314386fd7a2cb0afd1afcae6e0315ab951693
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2430184
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810709}

third_party/blink/renderer/core/layout/layout_box_model_object.cc

@@ -1101,22 +1101,23 @@ bool LayoutBoxModelObject::IsSlowRepaintConstrainedObject() const {
 }
 
 PhysicalRect LayoutBoxModelObject::ComputeStickyConstrainingRect() const {
-  LayoutBox* enclosing_clipping_box =
+  LayoutBox* scroll_container_box =
       Layer()->AncestorOverflowLayer()->GetLayoutBox();
-  DCHECK(enclosing_clipping_box);
+  DCHECK(scroll_container_box);
+  // That |scroll_container_box| is a scroll-container is ensured by
+  // Layer::AncestorOverflowLayer().
+  DCHECK(scroll_container_box->IsScrollContainer());
   PhysicalRect constraining_rect;
   constraining_rect =
-      PhysicalRect(enclosing_clipping_box->OverflowClipRect(LayoutPoint()));
-  constraining_rect.Move(
-      PhysicalOffset(-enclosing_clipping_box->BorderLeft() +
-                         enclosing_clipping_box->PaddingLeft(),
-                     -enclosing_clipping_box->BorderTop() +
-                         enclosing_clipping_box->PaddingTop()));
+      PhysicalRect(scroll_container_box->OverflowClipRect(LayoutPoint()));
+  constraining_rect.Move(PhysicalOffset(
+      -scroll_container_box->BorderLeft() + scroll_container_box->PaddingLeft(),
+      -scroll_container_box->BorderTop() + scroll_container_box->PaddingTop()));
   constraining_rect.ContractEdges(LayoutUnit(),
-                                  enclosing_clipping_box->PaddingLeft() +
-                                      enclosing_clipping_box->PaddingRight(),
-                                  enclosing_clipping_box->PaddingTop() +
-                                      enclosing_clipping_box->PaddingBottom(),
+                                  scroll_container_box->PaddingLeft() +
+                                      scroll_container_box->PaddingRight(),
+                                  scroll_container_box->PaddingTop() +
+                                      scroll_container_box->PaddingBottom(),
                                   LayoutUnit());
   return constraining_rect;
 }

third_party/blink/renderer/core/paint/compositing/compositing_inputs_updater.cc

@@ -95,8 +95,7 @@ void CompositingInputsUpdater::ApplyAncestorInfoToSelfAndAncestorsRecursively(
     geometry_map_->PushMappingsToAncestor(layer, layer->Parent());
   UpdateAncestorInfo(layer, update_type, info);
   if (layer != compositing_inputs_root_ &&
-      (layer->IsRootLayer() ||
-       layer->GetLayoutObject().HasNonVisibleOverflow()))
+      (layer->IsRootLayer() || layer->GetLayoutObject().IsScrollContainer()))
     info.last_overflow_clip_layer = layer;
 }
 
@@ -149,7 +148,7 @@ void CompositingInputsUpdater::UpdateSelfAndDescendantsRecursively(
       geometry_map_->PushMappingsToAncestor(layer, layer->Parent());
     UpdateAncestorInfo(layer, update_type, info);
   }
-  if (layer->IsRootLayer() || layout_object.HasNonVisibleOverflow())
+  if (layer->IsRootLayer() || layout_object.IsScrollContainer())
     info.last_overflow_clip_layer = layer;
 
   PaintLayerCompositor* compositor =