ISSUE-21803: implement ConstantSourceNode audionode

components/script/dom/webidls/ConstantSourceNode.webidl

@@ -0,0 +1,17 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+/*
+ * The origin of this IDL file is
+ * https://webaudio.github.io/web-audio-api/#ConstantSourceNode
+ */
+
+dictionary ConstantSourceOptions: AudioNodeOptions {
+  float offset = 1;
+};
+
+[Exposed=Window,
+ Constructor (BaseAudioContext context, optional ConstantSourceOptions options = {})]
+interface ConstantSourceNode : AudioScheduledSourceNode {
+  readonly attribute AudioParam offset;
+};