Add early return to NGOutOfFlowLayoutPart::Run()

Similar to what we have in NGOutOfFlowLayoutPart constructor
we should have an early return in NGOutOfFlowLayoutPart::Run()
when we have no positioned descendants.

We already have it a few lines later, but we can move it
to the beginning of the method to avoid any extra operation.

We also add a check for fragmentainer descendants to avoid
doing extra work if we don't have any.

BUG=1098231

Change-Id: I2d233c1c79a903d1696099c26029c2d09d59a728
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2279759Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Alison Maher <almaher@microsoft.com>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Manuel Rego <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#788556}

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

@@ -126,7 +126,8 @@ NGOutOfFlowLayoutPart::NGOutOfFlowLayoutPart(
 }
 
 void NGOutOfFlowLayoutPart::Run(const LayoutBox* only_layout) {
-  if (container_builder_->IsBlockFragmentationContextRoot()) {
+  if (container_builder_->IsBlockFragmentationContextRoot() &&
+      container_builder_->HasOutOfFlowFragmentainerDescendants()) {
     Vector<NGLogicalOutOfFlowPositionedNode> fragmentainer_descendants;
     container_builder_->SwapOutOfFlowFragmentainerDescendants(
         &fragmentainer_descendants);
@@ -135,20 +136,20 @@ void NGOutOfFlowLayoutPart::Run(const LayoutBox* only_layout) {
       LayoutFragmentainerDescendants(&fragmentainer_descendants);
   }
 
-  Vector<NGLogicalOutOfFlowPositionedNode> candidates;
   const LayoutObject* current_container = container_builder_->GetLayoutObject();
+  if (!container_builder_->HasOutOfFlowPositionedCandidates() &&
+      !To<LayoutBlock>(current_container)->HasPositionedObjects())
+    return;
+
   // If the container is display-locked, then we skip the layout of descendants,
   // so we can early out immediately.
   if (current_container->LayoutBlockedByDisplayLock(
           DisplayLockLifecycleTarget::kChildren))
     return;
 
+  Vector<NGLogicalOutOfFlowPositionedNode> candidates;
   container_builder_->SwapOutOfFlowPositionedCandidates(&candidates);
 
-  if (candidates.IsEmpty() &&
-      !To<LayoutBlock>(current_container)->HasPositionedObjects())
-    return;
-
   // Special case: containing block is a split inline.
   // If current container was generated by a split inline, do not position
   // OOF-positioned nodes inside this container. Let its non-anonymous parent