Upstream service worker `fetch` test to WPT

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/fetch-request-fallback-worker.js

-// TODO(horo): Service worker can be killed at some point during the test. So we
-// should use storage API instead of this global variable.
-var requests = [];
-
-self.addEventListener('message', function(event) {
-    event.data.port.postMessage({requests: requests});
-    requests = [];
-  });
-
-self.addEventListener('fetch', function(event) {
-    requests.push({
-        url: event.request.url,
-        mode: event.request.mode
-      });
-  });