Implement basic interface for MutationObserver and MutationRecord.

components/script/dom/webidls/MutationObserver.webidl

@@ -0,0 +1,27 @@
+/* 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/. */
+/*
+ * The origin of this IDL file is:
+ * https://dom.spec.whatwg.org/#mutationobserver
+ */
+
+// https://dom.spec.whatwg.org/#mutationobserver
+[Pref="dom.mutation_observer.enabled", Constructor(MutationCallback callback)]
+interface MutationObserver {
+    //void observe(Node target, optional MutationObserverInit options);
+    //void disconnect();
+    //sequence<MutationRecord> takeRecords();
+};
+
+callback MutationCallback = void (sequence<MutationRecord> mutations, MutationObserver observer);
+
+dictionary MutationObserverInit {
+    boolean childList = false;
+    boolean attributes;
+    boolean characterData;
+    boolean subtree = false;
+    boolean attributeOldValue;
+    boolean characterDataOldValue;
+    sequence<DOMString> attributeFilter;
+};