1 files changed, 15 insertions, 1 deletions
diff --git a/dom/base/CustomElementRegistry.h b/dom/base/CustomElementRegistry.h
index b5903f978..b85d089f9 100644
--- a/dom/base/CustomElementRegistry.h
+++ b/dom/base/CustomElementRegistry.h
@@ -128,6 +128,7 @@ struct CustomElementDefinition
   CustomElementDefinition(nsIAtom* aType,
                           nsIAtom* aLocalName,
                           Function* aConstructor,
+                          nsCOMArray<nsIAtom>&& aObservedAttributes,
                           JSObject* aPrototype,
                           mozilla::dom::LifecycleCallbacks* aCallbacks,
                           uint32_t aDocOrder);
@@ -141,6 +142,9 @@ struct CustomElementDefinition
   // The custom element constructor.
   RefPtr<CustomElementConstructor> mConstructor;
 
+  // The list of attributes that this custom element observes.
+  nsCOMArray<nsIAtom> mObservedAttributes;
+
   // The prototype to use for new custom elements of this type.
   JS::Heap<JSObject *> mPrototype;
 
@@ -153,9 +157,19 @@ struct CustomElementDefinition
   // The document custom element order.
   uint32_t mDocOrder;
 
-  bool IsCustomBuiltIn() {
+  bool IsCustomBuiltIn()
+  {
     return mType != mLocalName;
   }
+
+  bool IsInObservedAttributeList(nsIAtom* aName)
+  {
+    if (mObservedAttributes.IsEmpty()) {
+      return false;
+    }
+
+    return mObservedAttributes.Contains(aName);
+  }
 };
 
 class CustomElementReaction