[cleanup] Fix TODO in NGContainerFragmentBuilder.

Previously we didn't have a flag for elements which were painted
atomically. Now we do!

Use this flag, instead of the IsAtomicInline flag.

Change-Id: I33732fa995d928fc5f7d4e2984711d231a471ddb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2210001Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770646}

third_party/blink/renderer/core/layout/ng/ng_container_fragment_builder.cc

@@ -108,10 +108,9 @@ void NGContainerFragmentBuilder::PropagateChildData(
   // Compute |has_floating_descendants_for_paint_| to optimize tree traversal
   // in paint.
   if (!has_floating_descendants_for_paint_) {
-    // TODO(layout-dev): The |NGPhysicalFragment::IsAtomicInline| check should
-    // be checking for any children which paint all phases atomically.
     if (child.IsFloating() || child.IsLegacyLayoutRoot() ||
-        (child.HasFloatingDescendantsForPaint() && !child.IsAtomicInline()))
+        (child.HasFloatingDescendantsForPaint() &&
+         !child.IsPaintedAtomically()))
       has_floating_descendants_for_paint_ = true;
   }