Import w3c tests for the service workers

third_party/WebKit/LayoutTests/imported/wpt/service-workers/service-worker/resources/worker-load-interceptor.js

+importScripts('get-host-info.sub.js');
+
+var response_text = "This load was successfully intercepted.";
+var response_script = "postMessage(\"This load was successfully intercepted.\");";
+
+self.onfetch = function(event) {
+    var url = event.request.url;
+    if (url.indexOf("synthesized-response.txt") != -1) {
+        event.respondWith(new Response(response_text));
+    } else if (url.indexOf("synthesized-response.js") != -1) {
+        event.respondWith(new Response(response_script));
+    }
+};