Bug 1829335 - Add customElements.getName. r=smaug

This adds the new customElements.getName method which takes a constructor
and returns string if the definition has been registered, otherwise null.

Differential Revision: https://phabricator.services.mozilla.com/D181646

dom/base/CustomElementRegistry.cpp

@@ -1195,6 +1195,19 @@ void CustomElementRegistry::Get(
   aRetVal.SetAsCustomElementConstructor() = data->mConstructor;
 }
 
+void CustomElementRegistry::GetName(JSContext* aCx,
+                                    CustomElementConstructor& aConstructor,
+                                    nsAString& aResult) {
+  CustomElementDefinition* aDefinition =
+      LookupCustomElementDefinition(aCx, aConstructor.CallableOrNull());
+
+  if (aDefinition) {
+    aDefinition->mType->ToString(aResult);
+  } else {
+    aResult.SetIsVoid(true);
+  }
+}
+
 already_AddRefed<Promise> CustomElementRegistry::WhenDefined(
     const nsAString& aName, ErrorResult& aRv) {
   // Define a function that lazily creates a Promise and perform some action on

dom/base/CustomElementRegistry.h

@@ -557,6 +557,9 @@ class CustomElementRegistry final : public nsISupports, public nsWrapperCache {
   void Get(const nsAString& name,
            OwningCustomElementConstructorOrUndefined& aRetVal);
 
+  void GetName(JSContext* aCx, CustomElementConstructor& aConstructor,
+               nsAString& aResult);
+
   already_AddRefed<Promise> WhenDefined(const nsAString& aName,
                                         ErrorResult& aRv);
 

dom/bindings/Bindings.conf

@@ -180,7 +180,7 @@ DOMInterfaces = {
 },
 
 'CustomElementRegistry': {
-    'implicitJSContext': ['define'],
+    'implicitJSContext': ['define', 'getName'],
 },
 
 'DebuggerNotification': {

dom/webidl/CustomElementRegistry.webidl

@@ -11,6 +11,7 @@ interface CustomElementRegistry {
   [ChromeOnly, Throws]
   undefined setElementCreationCallback(DOMString name, CustomElementCreationCallback callback);
   (CustomElementConstructor or undefined) get(DOMString name);
+  DOMString? getName(CustomElementConstructor constructor);
   [Throws]
   Promise<CustomElementConstructor> whenDefined(DOMString name);
   [CEReactions] undefined upgrade(Node root);

testing/web-platform/meta/custom-elements/CustomElementRegistry.html.ini

@@ -1,9 +0,0 @@
-[CustomElementRegistry.html]
-  [customElements.getName must return null when the registry does not contain an entry with the given constructor]
-    expected: FAIL
-
-  [customElements.getName returns the name of the entry with the given constructor when there is a matching entry.]
-    expected: FAIL
-
-  [customElements.getName returns the name of the entry with the given customized built in constructor when there is a matching entry.]
-    expected: FAIL