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

third_party/WebKit/LayoutTests/imported/wpt/offscreen-canvas/line-styles/2d.line.miter.invalid.worker.js

-// DO NOT EDIT! This test has been generated by tools/gentest.py.
-// OffscreenCanvas test in a worker:2d.line.miter.invalid
-// Description:Setting miterLimit to invalid values is ignored
-// Note:
-
-importScripts("/resources/testharness.js");
-importScripts("/common/canvas-tests.js");
-
-var t = async_test("Setting miterLimit to invalid values is ignored");
-t.step(function() {
-
-var offscreenCanvas = new OffscreenCanvas(100, 50);
-var ctx = offscreenCanvas.getContext('2d');
-
-ctx.miterLimit = 1.5;
-_assertSame(ctx.miterLimit, 1.5, "ctx.miterLimit", "1.5");
-ctx.miterLimit = 1.5;
-ctx.miterLimit = 0;
-_assertSame(ctx.miterLimit, 1.5, "ctx.miterLimit", "1.5");
-ctx.miterLimit = 1.5;
-ctx.miterLimit = -1;
-_assertSame(ctx.miterLimit, 1.5, "ctx.miterLimit", "1.5");
-ctx.miterLimit = 1.5;
-ctx.miterLimit = Infinity;
-_assertSame(ctx.miterLimit, 1.5, "ctx.miterLimit", "1.5");
-ctx.miterLimit = 1.5;
-ctx.miterLimit = -Infinity;
-_assertSame(ctx.miterLimit, 1.5, "ctx.miterLimit", "1.5");
-ctx.miterLimit = 1.5;
-ctx.miterLimit = NaN;
-_assertSame(ctx.miterLimit, 1.5, "ctx.miterLimit", "1.5");
-
-t.done();
-
-});
-done();