Add offscreen-canvas to the list of wpt directories to skip.

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/drawing-rectangles-to-the-canvas/2d.strokeRect.globalcomposite.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.strokeRect.globalcomposite
-// Description:strokeRect is not affected by globalCompositeOperation
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("strokeRect is not affected by globalCompositeOperation");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.globalCompositeOperation = 'source-in';
-ctx.strokeStyle = '#f00';
-ctx.lineWidth = 50;
-ctx.strokeRect(25, 24, 50, 2);
-_assertPixel(offscreenCanvas, 50,25, 0,0,0,0, "50,25", "0,0,0,0");
-
-t.done();
-
-});
-done();