Set the fetch API request flags correctly for navigation requests.

LayoutTests/http/tests/serviceworker/resources/request-end-to-end-worker.js

 onfetch = function(e) {
   var headers = {};
   for (var header of e.request.headers) {
     var key = header[0], value = header[1];
     headers[key] = value;
   }
   var append_header_error = '';
   try {
     e.request.headers.append('Test-Header', 'TestValue');
   } catch (error) {
     append_header_error = error.name;
   }
 
   e.respondWith(new Response(JSON.stringify({
     url: e.request.url,
     method: e.request.method,
     referrer: e.request.referrer,
     headers: headers,
+    mode: e.request.mode,
+    credentials: e.request.credentials,
+    redirect: e.request.redirect,
     append_header_error: append_header_error
   })));
 };