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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/shadows/2d.shadow.alpha.1.worker.js

Index: third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/shadows/2d.shadow.alpha.1.worker.js
diff --git a/third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/shadows/2d.shadow.alpha.1.worker.js b/third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/shadows/2d.shadow.alpha.1.worker.js
deleted file mode 100644
index 9852033eed70cfac6e4b88c5cba8f66cac7dbbbc..0000000000000000000000000000000000000000
--- a/third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/shadows/2d.shadow.alpha.1.worker.js
+++ /dev/null
@@ -1,25 +0,0 @@
-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.shadow.alpha.1
-// Description:Shadow colour alpha components are used
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("Shadow colour alpha components are used");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.fillStyle = '#0f0';
-ctx.fillRect(0, 0, 100, 50);
-ctx.shadowColor = 'rgba(255, 0, 0, 0.01)';
-ctx.shadowOffsetY = 50;
-ctx.fillRect(0, -50, 100, 50);
-_assertPixelApprox(offscreenCanvas, 50,25, 0,255,0,255, "50,25", "0,255,0,255", 4);
-
-t.done();
-
-});
-done();