Bug 998590 - Cleanup HTMLHeadingElement, and add HTMLHeadingElement::FromNode. r=bzbarsky

Differential Revision: https://phabricator.services.mozilla.com/D49406

--HG--
extra : moz-landing-system : lando

dom/base/nsINode.h

@@ -746,6 +746,11 @@ class nsINode : public mozilla::dom::EventTarget {
     return isShadowRoot;
   }
 
+  bool IsHTMLHeadingElement() const {
+    return IsAnyOfHTMLElements(nsGkAtoms::h1, nsGkAtoms::h2, nsGkAtoms::h3,
+                               nsGkAtoms::h4, nsGkAtoms::h5, nsGkAtoms::h6);
+  }
+
   /**
    * Insert a content node before another or at the end.
    * This method handles calling BindToTree on the child appropriately.

dom/html/HTMLHeadingElement.h

@@ -17,15 +17,17 @@ class HTMLHeadingElement final : public nsGenericHTMLElement {
  public:
   explicit HTMLHeadingElement(
       already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
-      : nsGenericHTMLElement(std::move(aNodeInfo)) {}
+      : nsGenericHTMLElement(std::move(aNodeInfo)) {
+    MOZ_ASSERT(IsHTMLHeadingElement());
+  }
 
-  virtual bool ParseAttribute(int32_t aNamespaceID, nsAtom* aAttribute,
-                              const nsAString& aValue,
-                              nsIPrincipal* aMaybeScriptedPrincipal,
-                              nsAttrValue& aResult) override;
+  bool ParseAttribute(int32_t aNamespaceID, nsAtom* aAttribute,
+                      const nsAString& aValue,
+                      nsIPrincipal* aMaybeScriptedPrincipal,
+                      nsAttrValue& aResult) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsAtom* aAttribute) const override;
   nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
-  virtual nsresult Clone(dom::NodeInfo*, nsINode** aResult) const override;
+  nsresult Clone(dom::NodeInfo*, nsINode** aResult) const override;
 
   void SetAlign(const nsAString& aAlign, ErrorResult& aError) {
     return SetHTMLAttr(nsGkAtoms::align, aAlign, aError);
@@ -34,11 +36,12 @@ class HTMLHeadingElement final : public nsGenericHTMLElement {
     return GetHTMLAttr(nsGkAtoms::align, aAlign);
   }
 
+  NS_IMPL_FROMNODE_HELPER(HTMLHeadingElement, IsHTMLHeadingElement())
+
  protected:
   virtual ~HTMLHeadingElement();
 
-  virtual JSObject* WrapNode(JSContext* aCx,
-                             JS::Handle<JSObject*> aGivenProto) override;
+  JSObject* WrapNode(JSContext*, JS::Handle<JSObject*> aGivenProto) override;
 
  private:
   static void MapAttributesIntoRule(const nsMappedAttributes* aAttributes,