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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/line-styles/2d.line.miter.within.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.line.miter.within
-// Description:Miter joins are drawn when the miter limit is not quite exceeded
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("Miter joins are drawn when the miter limit is not quite exceeded");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.fillStyle = '#f00';
-ctx.fillRect(0, 0, 100, 50);
-ctx.lineWidth = 400;
-ctx.lineJoin = 'miter';
-ctx.strokeStyle = '#0f0';
-ctx.miterLimit = 1.416;
-ctx.beginPath();
-ctx.moveTo(200, 1000);
-ctx.lineTo(200, 200);
-ctx.lineTo(1000, 201);
-ctx.stroke();
-_assertPixel(offscreenCanvas, 1,1, 0,255,0,255, "1,1", "0,255,0,255");
-_assertPixel(offscreenCanvas, 48,1, 0,255,0,255, "48,1", "0,255,0,255");
-_assertPixel(offscreenCanvas, 48,48, 0,255,0,255, "48,48", "0,255,0,255");
-_assertPixel(offscreenCanvas, 1,48, 0,255,0,255, "1,48", "0,255,0,255");
-
-t.done();
-
-});
-done();