Bug 1637307 - Push/Pop dialog to top layer when needed r=smaug

This patch completes the top layer requirement for showModal()
Spec: https://html.spec.whatwg.org/multipage/interactive-elements.html#dom-dialog-showmodal

Differential Revision: https://phabricator.services.mozilla.com/D74922

dom/base/Document.cpp

@@ -13415,6 +13415,17 @@ Element* Document::GetTopLayerTop() {
   return element;
 }
 
+bool Document::DoesTopLayerContain(const Element* aElement) const {
+  for (const nsWeakPtr& weakPtr : mTopLayer) {
+    nsCOMPtr<Element> element(do_QueryReferent(weakPtr));
+    if (element && element == aElement) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 Element* Document::GetUnretargetedFullScreenElement() {
   for (const nsWeakPtr& weakPtr : Reversed(mTopLayer)) {
     nsCOMPtr<Element> element(do_QueryReferent(weakPtr));

dom/base/Document.h

@@ -3405,6 +3405,9 @@ class Document : public nsINode,
   // Not const because all the fullscreen goop is not const
   bool FullscreenEnabled(CallerType aCallerType);
   Element* GetTopLayerTop();
+
+  bool DoesTopLayerContain(const Element* aElement) const;
+
   // Return the fullscreen element in the top layer
   Element* GetUnretargetedFullScreenElement();
   bool Fullscreen() { return !!GetFullscreenElement(); }

dom/html/HTMLDialogElement.cpp

@@ -44,6 +44,13 @@ void HTMLDialogElement::Close(
   ErrorResult ignored;
   SetOpen(false, ignored);
   ignored.SuppressException();
+
+  Document* doc = OwnerDoc();
+  auto predictFunc = [self = RefPtr<HTMLDialogElement>(this)](
+                         Element* element) { return element == self; };
+
+  doc->TopLayerPop(predictFunc);
+
   RefPtr<AsyncEventDispatcher> eventDispatcher = new AsyncEventDispatcher(
       this, NS_LITERAL_STRING("close"), CanBubble::eNo);
   eventDispatcher->PostDOMEvent();
@@ -58,12 +65,32 @@ void HTMLDialogElement::Show() {
   ignored.SuppressException();
 }
 
+bool HTMLDialogElement::IsInTopLayer() const {
+  return OwnerDoc()->DoesTopLayerContain(this);
+}
+
+void HTMLDialogElement::UnbindFromTree(bool aNullParent) {
+  if (IsInTopLayer()) {
+    Document* doc = OwnerDoc();
+    auto predictFunc = [self = RefPtr<HTMLDialogElement>(this)](
+                           Element* element) { return element == self; };
+
+    doc->TopLayerPop(predictFunc);
+  }
+  nsGenericHTMLElement::UnbindFromTree(aNullParent);
+}
+
 void HTMLDialogElement::ShowModal(ErrorResult& aError) {
   if (!IsInComposedDoc() || Open()) {
     aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
     return;
   }
 
+  Document* doc = OwnerDoc();
+  if (!IsInTopLayer()) {
+    doc->TopLayerPush(this);
+  }
+
   SetOpen(true, aError);
   aError.SuppressException();
 }

dom/html/HTMLDialogElement.h

@@ -37,10 +37,14 @@ class HTMLDialogElement final : public nsGenericHTMLElement {
     mReturnValue = aReturnValue;
   }
 
+  virtual void UnbindFromTree(bool aNullParent = true) override;
+
   void Close(const mozilla::dom::Optional<nsAString>& aReturnValue);
   void Show();
   void ShowModal(ErrorResult& aError);
 
+  bool IsInTopLayer() const;
+
   nsString mReturnValue;
 
  protected: