Sets the parent of an AXVirtualObject when adding its children

This is the only remaining occasion, as far as I can tell, where we
are still forgetting to set the parent of a child object properly.
All other cases have been fixed either by my previous patches or by
patches recently authored by aleventhal@.
Also added a few DCHECKs in AXSlider and AXMenuList.

AX-Relnotes: n/a.

R=dmazzoni@chromium.org, aleventhal@chromium.org

Change-Id: I22af3f276cc325a71968f6b2956d17120ce03320
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2356484
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820752}

third_party/blink/renderer/modules/accessibility/ax_menu_list.cc

@@ -74,15 +74,15 @@ void AXMenuList::AddChildren() {
   have_children_ = true;
 
   AXObjectCacheImpl& cache = AXObjectCache();
-
   AXObject* popup = cache.Create(ax::mojom::blink::Role::kMenuListPopup, this);
+  DCHECK(popup);
+
   if (!popup->AccessibilityIsIncludedInTree()) {
     cache.Remove(popup->AXObjectID());
     return;
   }
 
   children_.push_back(popup);
-
   popup->AddChildren();
 }
 

third_party/blink/renderer/modules/accessibility/ax_menu_list_popup.cc

@@ -109,8 +109,8 @@ void AXMenuListPopup::AddChildren() {
   for (auto* const option_element : html_select_element->GetOptionList()) {
     AXMenuListOption* option = MenuListOptionAXObject(option_element);
     if (option) {
-      option->SetParent(this);
       children_.push_back(option);
+      option->SetParent(this);
     }
   }
 }

third_party/blink/renderer/modules/accessibility/ax_slider.cc

@@ -78,23 +78,24 @@ AccessibilityOrientation AXSlider::Orientation() const {
 void AXSlider::AddChildren() {
   DCHECK(!IsDetached());
   DCHECK(!have_children_);
-
   have_children_ = true;
 
   AXObjectCacheImpl& cache = AXObjectCache();
-
   AXObject* thumb = cache.Create(ax::mojom::blink::Role::kSliderThumb, this);
+  DCHECK(thumb);
 
   // Before actually adding the value indicator to the hierarchy,
   // allow the platform to make a final decision about it.
-  if (!thumb->AccessibilityIsIncludedInTree())
+  if (!thumb->AccessibilityIsIncludedInTree()) {
     cache.Remove(thumb->AXObjectID());
-  else
-    children_.push_back(thumb);
+    return;
+  }
+
+  children_.push_back(thumb);
 }
 
 AXObject* AXSlider::ElementAccessibilityHitTest(const IntPoint& point) const {
-  if (children_.size()) {
+  if (HasChildren()) {
     DCHECK(children_.size() == 1);
     if (children_[0]->GetBoundsInFrameCoordinates().Contains(point))
       return children_[0].Get();

third_party/blink/renderer/modules/accessibility/ax_virtual_object.cc

@@ -29,8 +29,14 @@ void AXVirtualObject::AddChildren() {
   if (!accessible_node_)
     return;
 
-  for (const auto& child : accessible_node_->GetChildren())
-    children_.push_back(AXObjectCache().GetOrCreate(child));
+  for (const auto& child : accessible_node_->GetChildren()) {
+    AXObject* ax_child = AXObjectCache().GetOrCreate(child);
+    if (!ax_child)
+      continue;
+
+    children_.push_back(ax_child);
+    ax_child->SetParent(this);
+  }
 }
 
 void AXVirtualObject::ChildrenChanged() {