Revert of [ServivceWorker] Treat rejecting respondWith as a Network Error

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

Index: LayoutTests/http/tests/serviceworker/fetch-event.html
diff --git a/LayoutTests/http/tests/serviceworker/fetch-event.html b/LayoutTests/http/tests/serviceworker/fetch-event.html
index e51dcb1f24fc8025a9bd894c15ca9f5804cae2ef..e7c6bac6e40c2251dc3b2c458cdc661935396c20 100644
--- a/LayoutTests/http/tests/serviceworker/fetch-event.html
+++ b/LayoutTests/http/tests/serviceworker/fetch-event.html
@@ -105,8 +105,8 @@
       .then(function() { return with_iframe(scope); })
       .then(function(frame) {
           assert_equals(frame.contentDocument.body.textContent,
-                        '',
-                        'Response should be a NetworkError');
+                        'Here\'s a simple html file.\n',
+                        'Response should come from fallback to native fetch');
           unload_iframe(frame);
           return service_worker_unregister_and_done(t, scope);
         })