Implemented Houdini worklets.

components/script/dom/webidls/Worklet.webidl

@@ -0,0 +1,13 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// https://drafts.css-houdini.org/worklets/#worklet
+[Exposed=(Window)]
+interface Worklet {
+    [NewObject] Promise<void> addModule(USVString moduleURL, optional WorkletOptions options);
+};
+
+dictionary WorkletOptions {
+    RequestCredentials credentials = "omit";
+};