Add layout tests to check that a FetchEvent includes the right headers

third_party/WebKit/LayoutTests/http/tests/serviceworker/fetch-event.html

Index: third_party/WebKit/LayoutTests/http/tests/serviceworker/fetch-event.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/serviceworker/fetch-event.html b/third_party/WebKit/LayoutTests/http/tests/serviceworker/fetch-event.html
index a27c2b9490fdff21e50bdaec2743070d49166626..496a24028bb63d67cb1e26d9199832def2ff0044 100644
--- a/third_party/WebKit/LayoutTests/http/tests/serviceworker/fetch-event.html
+++ b/third_party/WebKit/LayoutTests/http/tests/serviceworker/fetch-event.html
@@ -7,6 +7,34 @@
 var worker = 'resources/fetch-event-test-worker.js';
 
 async_test(function(t) {
+    const scope = 'resources/simple.html?headers';
+    service_worker_unregister_and_register(t, worker, scope)
+      .then(function(reg) {
+          return wait_for_state(t, reg.installing, 'activated');
+        })
+      .then(function() { return with_iframe(scope); })
+      .then(function(frame) {
+          // We have this test to prevent unexpected exposure of headers to a
+          // ServiceWorker. Feel free to rebaseline this expectation if it
+          // looks good.
+          const headers = JSON.parse(frame.contentDocument.body.textContent);
+          const header_names = [];
+          for (const [name, value] of headers) {
+            header_names.push(name);
+          }
+          header_names.sort();
+          assert_array_equals(
+            header_names,
+            ["accept", "upgrade-insecure-requests", "user-agent"],
+            'event.request has the expected headers.');
+
+          frame.remove();
+          return service_worker_unregister_and_done(t, scope);
+        })
+      .catch(unreached_rejection(t));
+  }, 'Service Worker headers in the request of a fetch event');
+
+async_test(function(t) {
     var scope = 'resources/simple.html?string';
     service_worker_unregister_and_register(t, worker, scope)
       .then(function(reg) {