[ServiceWorker] Set FetchRequestMode and handle wasFetchedViaServiceWorker.

LayoutTests/http/tests/serviceworker/resources/fetch-request-xhr-worker.js

Index: LayoutTests/http/tests/serviceworker/resources/fetch-request-xhr-worker.js
diff --git a/LayoutTests/http/tests/serviceworker/resources/fetch-request-xhr-worker.js b/LayoutTests/http/tests/serviceworker/resources/fetch-request-xhr-worker.js
index f21a86320017c8cc8a37eb283e59cab9ebe8f123..a7d6563c88132f707729f2e72f1bb2a74ee2bab2 100644
--- a/LayoutTests/http/tests/serviceworker/resources/fetch-request-xhr-worker.js
+++ b/LayoutTests/http/tests/serviceworker/resources/fetch-request-xhr-worker.js
@@ -12,6 +12,7 @@ self.addEventListener('fetch', function(event) {
           .then(function(result) {
               resolve(new Response(JSON.stringify({
                   method: event.request.method,
+                  mode: event.request.mode,

[yhirano, 2014/10/08 09:31:39]

Maybe this will be used for the request mode transfer and can be removed from
this CL?

[horo, 2014/10/08 10:02:47]

This is used from mode_test() in fetch-request-xhr-iframe.html.
This test checks that the all FetchEvent's request mode from XHR must be "cors".

                   headers: headers,
                   body: result
                 })));