Bug 1319255 part 2. Stop doing casts to HTMLContentElement* simply based on tag. r=wchen

dom/base/ChildIterator.cpp

@@ -60,7 +60,7 @@ GetMatchedNodesForPoint(nsIContent* aContent)
 
   // Web components case
   MOZ_ASSERT(aContent->IsHTMLElement(nsGkAtoms::content));
-  return MatchedNodes(static_cast<HTMLContentElement*>(aContent));
+  return MatchedNodes(HTMLContentElement::FromContent(aContent));
 }
 
 nsIContent*

dom/base/ShadowRoot.cpp

@@ -595,10 +595,11 @@ ShadowRoot::IsPooledNode(nsIContent* aContent, nsIContent* aContainer,
     return true;
   }
 
-  if (aContainer && aContainer->IsHTMLElement(nsGkAtoms::content)) {
+  if (aContainer) {
     // Fallback content will end up in pool if its parent is a child of the host.
-    HTMLContentElement* content = static_cast<HTMLContentElement*>(aContainer);
+    HTMLContentElement* content = HTMLContentElement::FromContent(aContainer);
-    return content->IsInsertionPoint() && content->MatchedNodes().IsEmpty() &&
+    return content && content->IsInsertionPoint() &&
+           content->MatchedNodes().IsEmpty() &&
            aContainer->GetParentNode() == aHost;
   }
 
@@ -640,7 +641,7 @@ ShadowRoot::ContentAppended(nsIDocument* aDocument,
   while (currentChild) {
     // Add insertion point to destination insertion points of fallback content.
     if (nsContentUtils::IsContentInsertionPoint(aContainer)) {
-      HTMLContentElement* content = static_cast<HTMLContentElement*>(aContainer);
+      HTMLContentElement* content = HTMLContentElement::FromContent(aContainer);
       if (content->MatchedNodes().IsEmpty()) {
         currentChild->DestInsertionPoints().AppendElement(aContainer);
       }
@@ -671,7 +672,7 @@ ShadowRoot::ContentInserted(nsIDocument* aDocument,
   if (IsPooledNode(aChild, aContainer, mPoolHost)) {
     // Add insertion point to destination insertion points of fallback content.
     if (nsContentUtils::IsContentInsertionPoint(aContainer)) {
-      HTMLContentElement* content = static_cast<HTMLContentElement*>(aContainer);
+      HTMLContentElement* content = HTMLContentElement::FromContent(aContainer);
       if (content->MatchedNodes().IsEmpty()) {
         aChild->DestInsertionPoints().AppendElement(aContainer);
       }
@@ -697,7 +698,7 @@ ShadowRoot::ContentRemoved(nsIDocument* aDocument,
   // Clear destination insertion points for removed
   // fallback content.
   if (nsContentUtils::IsContentInsertionPoint(aContainer)) {
-    HTMLContentElement* content = static_cast<HTMLContentElement*>(aContainer);
+    HTMLContentElement* content = HTMLContentElement::FromContent(aContainer);
     if (content->MatchedNodes().IsEmpty()) {
       aChild->DestInsertionPoints().Clear();
     }

dom/base/nsContentUtils.cpp

@@ -7063,7 +7063,7 @@ nsContentUtils::GetHTMLEditor(nsPresContext* aPresContext)
 }
 
 bool
-nsContentUtils::IsContentInsertionPoint(const nsIContent* aContent)
+nsContentUtils::IsContentInsertionPoint(nsIContent* aContent)
 {
   // Check if the content is a XBL insertion point.
   if (aContent->IsActiveChildrenElement()) {
@@ -7071,11 +7071,9 @@ nsContentUtils::IsContentInsertionPoint(const nsIContent* aContent)
   }
 
   // Check if the content is a web components content insertion point.
-  if (aContent->IsHTMLElement(nsGkAtoms::content)) {
+  HTMLContentElement* contentElement =
-    return static_cast<const HTMLContentElement*>(aContent)->IsInsertionPoint();
+    HTMLContentElement::FromContent(aContent);
-  }
+  return contentElement && contentElement->IsInsertionPoint();
-
-  return false;
 }
 
 // static

dom/base/nsContentUtils.h

@@ -2412,7 +2412,7 @@ public:
    *
    * @param aContent The content to test for being an insertion point.
    */
-  static bool IsContentInsertionPoint(const nsIContent* aContent);
+  static bool IsContentInsertionPoint(nsIContent* aContent);
 
 
   /**

dom/base/nsINode.h

@@ -1329,6 +1329,10 @@ public:
   // a way to ask an element whether it's an HTMLShadowElement.
   virtual bool IsHTMLShadowElement() const { return false; }
 
+  // Elements named <content> may or may not be HTMLContentElement.  This is a
+  // way to ask an element whether it's an HTMLContentElement.
+  virtual bool IsHTMLContentElement() const { return false; }
+
 protected:
   nsIURI* GetExplicitBaseURI() const {
     if (HasExplicitBaseURI()) {

dom/html/HTMLContentElement.cpp

@@ -66,7 +66,7 @@ HTMLContentElement::BindToTree(nsIDocument* aDocument,
   if (containingShadow && !oldContainingShadow) {
     nsINode* parentNode = nsINode::GetParentNode();
     while (parentNode && parentNode != containingShadow) {
-      if (parentNode->IsHTMLElement(nsGkAtoms::content)) {
+      if (parentNode->IsHTMLContentElement()) {
         // Content element in fallback content is not an insertion point.
         return NS_OK;
       }

dom/html/HTMLContentElement.h

@@ -23,14 +23,23 @@ class HTMLContentElement final : public nsGenericHTMLElement
 public:
   explicit HTMLContentElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo);
 
-  NS_IMPL_FROMCONTENT_HTML_WITH_TAG(HTMLContentElement, content)
-
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
 
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLContentElement,
                                            nsGenericHTMLElement)
 
+  static HTMLContentElement* FromContent(nsIContent* aContent)
+  {
+    if (aContent->IsHTMLContentElement()) {
+      return static_cast<HTMLContentElement*>(aContent);
+    }
+
+    return nullptr;
+  }
+
+  virtual bool IsHTMLContentElement() const override { return true; }
+
   virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
 
   virtual nsIDOMNode* AsDOMNode() override { return this; }