Added webidl file for OffscreenCanvas

components/script/dom/webidls/OffscreenCanvas.webidl

@@ -0,0 +1,29 @@
+/* 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/. */
+
+
+
+typedef (OffscreenCanvasRenderingContext2D or WebGLRenderingContext or WebGL2RenderingContext) OffscreenRenderingContext;
+
+dictionary ImageEncodeOptions {
+  DOMString type = "image/png";
+  unrestricted double quality = 1.0;
+};
+
+enum OffscreenRenderingContextId { "2d", "webgl", "webgl2" };
+
+[Constructor([EnforceRange] unsigned long long width, [EnforceRange] unsigned long long height), Exposed=(Window,Worker), Transferable]
+[Pref="dom.offscreen_canvas.enabled"]
+interface OffscreenCanvas : EventTarget {
+  attribute [EnforceRange] unsigned long long width;
+  attribute [EnforceRange] unsigned long long height;
+
+  OffscreenRenderingContext? getContext(OffscreenRenderingContextId contextId, optional any options = null);
+  ImageBitmap transferToImageBitmap();
+  //Promise<Blob> convertToBlob(optional ImageEncodeOptions options);
+};
+
+
+
+