[ServiceWorker] Make fetch() method better conformance with the spec.

LayoutTests/http/tests/serviceworker/resources/fetch-access-control-iframe.html

Index: LayoutTests/http/tests/serviceworker/resources/fetch-access-control-iframe.html
diff --git a/LayoutTests/http/tests/serviceworker/resources/fetch-access-control-iframe.html b/LayoutTests/http/tests/serviceworker/resources/fetch-access-control-iframe.html
new file mode 100644
index 0000000000000000000000000000000000000000..a9de7d22fb49b30365a25cac120ff878d7adffb5
--- /dev/null
+++ b/LayoutTests/http/tests/serviceworker/resources/fetch-access-control-iframe.html
@@ -0,0 +1,19 @@
+<script>
+function onMessage(event) {
+    var script = document.createElement('script');
+    script.src = event.data.url;
+    script.addEventListener(
+        'error',
+        function() { report({jsonpResult:'error'}); });
+    document.body.appendChild(script);
+}
+function report(data) {
+    window.parent.postMessage(
+        data,
+        'http://127.0.0.1:8000');
+}
+function onload() {
+    window.addEventListener('message', onMessage, false);
+}
+window.addEventListener('load', onload);
+</script>