Make OffscreenCanvasRenderingContext2D renderable on a worker

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.idl

 // Copyright 2016 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.
 
 // Note: The official spec is WIP at wiki.whatwg.org/wiki/OffscreenCanvas.
 
 [
     GarbageCollected,
     Exposed=(Window,Worker),
     RuntimeEnabled=ExperimentalCanvasFeatures,
 ] interface OffscreenCanvasRenderingContext2D {
     // back-reference to the canvas
     [ImplementedAs=getOffscreenCanvas] readonly attribute OffscreenCanvas offscreenCanvas;
+
+    // colors and styles (see also the CanvasDrawingStyles interface)
+    attribute (DOMString or CanvasGradient or CanvasPattern) strokeStyle; // (default black)
+    attribute (DOMString or CanvasGradient or CanvasPattern) fillStyle; // (default black)
+
+    //CanvasRect interface
+    void clearRect(unrestricted double x, unrestricted double y, unrestricted double width, unrestricted double height);
+    void fillRect(unrestricted double x, unrestricted double y, unrestricted double width, unrestricted double height);
+    void strokeRect(unrestricted double x, unrestricted double y, unrestricted double width, unrestricted double height);
 };
 
 OffscreenCanvasRenderingContext2D implements CanvasPathMethods;