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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/fill-and-stroke-styles/2d.fillStyle.parse.system.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.fillStyle.parse.system
-// Description:
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-
-ctx.fillStyle = '#f00';
-ctx.fillStyle = 'ThreeDDarkShadow';
-assert_regexp_match(ctx.fillStyle, /^#(?!(FF0000|ff0000|f00)$)/); // test that it's not red
-
-t.done();
-
-});
-done();