Start an empty interface OffScreenCanvas

third_party/WebKit/Source/core/html/canvas/OffScreenCanvas.idl

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://wiki.whatwg.org/wiki/OffscreenCanvas
+
+[
+    Constructor(unsigned long width, unsigned long height),
+    Exposed=(Window,Worker),
+    GarbageCollected,
+    RuntimeEnabled=ExperimentalCanvasFeatures,
+] interface OffScreenCanvas {
+    attribute unsigned long width;
+    attribute unsigned long height;
+    // RenderingContext? getContext(DOMString contextId, any... arguments);
+    ImageBitmap transferToImageBitmap();
+    // Promise<Blob> toBlob(optional DOMString type, any... arguments);
+};
+
+// TODO(crbug.com/547054): fix this once the Transferable base class is available.
+// OffscreenCanvas implements Transferable;
+// ImageBitmap implements Transferable;