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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/pixel-manipulation/2d.imageData.create2.initial.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.imageData.create2.initial
-// Description:createImageData(sw, sh) returns transparent black data of the right size
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("createImageData(sw, sh) returns transparent black data of the right size");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-var imgdata = ctx.createImageData(10, 20);
-_assertSame(imgdata.data.length, imgdata.width*imgdata.height*4, "imgdata.data.length", "imgdata.width*imgdata.height*4");
-_assert(imgdata.width < imgdata.height, "imgdata.width < imgdata.height");
-_assert(imgdata.width > 0, "imgdata.width > 0");
-var isTransparentBlack = true;
-for (var i = 0; i < imgdata.data.length; ++i)
-    if (imgdata.data[i] !== 0)
-        isTransparentBlack = false;
-_assert(isTransparentBlack, "isTransparentBlack");
-
-t.done();
-
-});
-done();