[ServiceWorker] Add test for FetchEvent's body with a local file.

LayoutTests/http/tests/local/serviceworker/resources/fetch-request-body-file-iframe.html

+<script src="../../../resources/testharness.js"></script>
+<script src="../../../serviceworker/resources/test-helpers.js?pipe=sub"></script>
+<script>
+var port = undefined;
+var scope = 'fetch-request-body-file-test';
+var script = 'fetch-request-body-file-worker.js';
+
+window.addEventListener('message', function(evt) {
+    port = evt.ports[0];
+    start();
+  }, false);
+
+function start() {
+  if (location.search == '?register') {
+    async_test(function(t) {

[nhiroki, 2014/08/27 03:52:34]

Would it be possible to remove async_test() from here?

[horo, 2014/08/27 05:05:45]

I introduced this in order to use wait_for_update as your comment in patch set
1.

[nhiroki, 2014/08/27 05:23:21]

I see... I didn't mean to reuse the wait_for_update() in test_helper.js. The
comment wanted to say "how about making a separate function like
wait_for_update() in this file?". Sorry for my ambiguous comment.

[horo, 2014/08/27 06:01:54]

Done.

+        service_worker_unregister_and_register(t, script, scope)

[nhiroki, 2014/08/27 03:52:34]

Question: Why don't you call register()/unregister() in
fetch-request-body-file.html? Does this file exist in a different origin?

[horo, 2014/08/27 05:05:45]

In layouttest, fetch-request-body-file.html is opened as a local file.
So to register a ServiceWorker we have to open this file on HTTP server.

[nhiroki, 2014/08/27 05:23:21]

Acknowledged.

+          .then(function(registration) {
+              return wait_for_update(t, registration);
+            })
+          .then(function(worker) {
+              port.postMessage({msg: 'registered'});
+            })
+          .catch(function() {
+              port.postMessage({msg: 'registration error'});
+            });
+      }, 'Register ServiceWorker');
+  } else if (location.search == '?unregister') {
+    async_test(function(t) {

[nhiroki, 2014/08/27 03:52:34]

ditto (removing async_test).

+        navigator.serviceWorker.register(script, {scope: scope})
+          .then(function(registration) {
+              return registration.unregister();
+            })
+          .then(function() {
+              port.postMessage({msg: 'unregistered'});
+            })
+          .catch(function() {
+              port.postMessage({msg: 'unregistration error'});
+            });
+      }, 'Unregister ServiceWorker');
+  }
+}
+</script>