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

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

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.line.width.valid
-// Description:Setting lineWidth to valid values works
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("Setting lineWidth to valid values works");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.lineWidth = 1.5;
-_assertSame(ctx.lineWidth, 1.5, "ctx.lineWidth", "1.5");
-ctx.lineWidth = "1e1";
-_assertSame(ctx.lineWidth, 10, "ctx.lineWidth", "10");
-ctx.lineWidth = 1/1024;
-_assertSame(ctx.lineWidth, 1/1024, "ctx.lineWidth", "1/1024");
-ctx.lineWidth = 1000;
-_assertSame(ctx.lineWidth, 1000, "ctx.lineWidth", "1000");
-
-t.done();
-
-});
-done();