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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/pixel-manipulation/2d.imageData.create1.initial.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.imageData.create1.initial
-// Description:createImageData(imgdata) returns transparent black data of the right size
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("createImageData(imgdata) returns transparent black data of the right size");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.fillStyle = '#0f0';
-ctx.fillRect(0, 0, 100, 50);
-var imgdata1 = ctx.getImageData(0, 0, 10, 20);
-var imgdata2 = ctx.createImageData(imgdata1);
-_assertSame(imgdata2.data.length, imgdata1.data.length, "imgdata2.data.length", "imgdata1.data.length");
-_assertSame(imgdata2.width, imgdata1.width, "imgdata2.width", "imgdata1.width");
-_assertSame(imgdata2.height, imgdata1.height, "imgdata2.height", "imgdata1.height");
-var isTransparentBlack = true;
-for (var i = 0; i < imgdata2.data.length; ++i)
-    if (imgdata2.data[i] !== 0)
-        isTransparentBlack = false;
-_assert(isTransparentBlack, "isTransparentBlack");
-
-t.done();
-
-});
-done();