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

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

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.imageData.get.range
-// Description:getImageData() returns values in the range [0, 255]
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("getImageData() returns values in the range [0, 255]");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.fillStyle = '#000';
-ctx.fillRect(0, 0, 100, 50);
-ctx.fillStyle = '#fff';
-ctx.fillRect(20, 10, 60, 10);
-var imgdata1 = ctx.getImageData(10, 5, 1, 1);
-_assertSame(imgdata1.data[0], 0, "imgdata1.data[\""+(0)+"\"]", "0");
-var imgdata2 = ctx.getImageData(30, 15, 1, 1);
-_assertSame(imgdata2.data[0], 255, "imgdata2.data[\""+(0)+"\"]", "255");
-
-t.done();
-
-});
-done();