ServiceWorker: Add t.add_cleanup() in WPT tests.

This CL adds t.add_cleanup() that calls service_worker_unregister()
in WPT tests to ensure registrations are removed on test completion.

Bug: 824647
Change-Id: Ieb790d4d7f63fc4810f6062d7e288aad1e88f45d
Reviewed-on: https://chromium-review.googlesource.com/c/1328545
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608693}

AUTHORS

@@ -96,6 +96,7 @@ Arun Mankuzhi <arun.m@samsung.com>
 Arunoday Sarkar <a.sarkar.arun@gmail.com>
 Arunprasad Rajkumar <ararunprasad@gmail.com>
 Arunprasad Rajkumar <arurajku@cisco.com>
+Asami Doi <d0iasm.pub@gmail.com>
 Ashish Kumar Gupta <guptaag@amazon.com>
 Ashlin Joseph <ashlin.j@samsung.com>
 Asish Singh <asish.singh@samsung.com>

third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/import-module-scripts.https.html

@@ -13,6 +13,7 @@ function import_test(testCase) {
       navigator.serviceWorker.onmessage = resolve;
     });
     await service_worker_unregister(t, testCase.scriptURL);
+    t.add_cleanup(() => service_worker_unregister(t, testCase.scriptURL));
     const registration = await navigator.serviceWorker.register(
       testCase.scriptURL,
       { scope: testCase.scriptURL, type: 'module' });