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.zero.4.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.strokeRect.zero.4
-// Description:strokeRect of Nx0 pixels draws a closed line with no caps
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("strokeRect of Nx0 pixels draws a closed line with no caps");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.strokeStyle = '#f00';
-ctx.lineWidth = 250;
-ctx.lineCap = 'round';
-ctx.strokeRect(100, 25, 100, 0);
-_assertPixel(offscreenCanvas, 50,25, 0,0,0,0, "50,25", "0,0,0,0");
-
-t.done();
-
-});
-done();