Upstream service worker "request" tests to WPT

third_party/WebKit/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;
   }
 
   var request_construct_error = '';
   try {
     new Request(e.request, {method: 'GET'});
   } catch (error) {
     request_construct_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,
     request_construct_error: request_construct_error
   })));
 };