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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/drawing-images-to-the-canvas/2d.drawImage.canvas.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.drawImage.canvas
-// 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');
-
-var offscreenCanvas2 = new OffscreenCanvas(100, 50);
-var ctx2 = offscreenCanvas2.getContext('2d');
-ctx2.fillStyle = '#0f0';
-ctx2.fillRect(0, 0, 100, 50);
-ctx.fillStyle = '#f00';
-ctx.drawImage(offscreenCanvas2, 0, 0);
-_assertPixelApprox(offscreenCanvas, 0,0, 0,255,0,255, "0,0", "0,255,0,255", 2);
-_assertPixelApprox(offscreenCanvas, 99,0, 0,255,0,255, "99,0", "0,255,0,255", 2);
-_assertPixelApprox(offscreenCanvas, 0,49, 0,255,0,255, "0,49", "0,255,0,255", 2);
-_assertPixelApprox(offscreenCanvas, 99,49, 0,255,0,255, "99,49", "0,255,0,255", 2);
-
-t.done();
-
-});
-done();