Add createGradient and createPattern to OffscreenCanvas2D in 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.
 
 [
     Exposed=(Window,Worker),
     RuntimeEnabled=ExperimentalCanvasFeatures,
 ] interface OffscreenCanvasRenderingContext2D {
     // back-reference to the canvas
     [ImplementedAs=getOffscreenCanvas] readonly attribute OffscreenCanvas offscreenCanvas;
 
     // colors and styles
     attribute (DOMString or CanvasGradient or CanvasPattern) strokeStyle; // (default black)
     attribute (DOMString or CanvasGradient or CanvasPattern) fillStyle; // (default black)
+    CanvasGradient createLinearGradient(double x0, double y0, double x1, double y1);
+    [RaisesException] CanvasGradient createRadialGradient(double x0, double y0, double r0, double x1, double y1, double r1);
+    [CallWith=ScriptState, RaisesException, Exposed=Worker] CanvasPattern? createPattern(CanvasImageSource image, [TreatNullAs=NullString] DOMString repetitionType);
 
     // 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);
 
     // Path API (See BaseRenderingContext2D)
     void beginPath();
     void fill(optional CanvasFillRule winding);
     void fill(Path2D path, optional CanvasFillRule winding);
@@ skipping 24 matching lines @@
     void resetTransform();
 
     // shadows
     attribute unrestricted double shadowOffsetX;
     attribute unrestricted double shadowOffsetY;
     attribute unrestricted double shadowBlur;
     attribute DOMString shadowColor;
 };
 
 OffscreenCanvasRenderingContext2D implements CanvasPathMethods;