Start implementing ForeignFetchEvent for foreign fetch events.

third_party/WebKit/Source/modules/serviceworkers/ForeignFetchResponse.idl

Index: third_party/WebKit/Source/modules/serviceworkers/ForeignFetchResponse.idl
diff --git a/third_party/WebKit/Source/modules/serviceworkers/FetchEventInit.idl b/third_party/WebKit/Source/modules/serviceworkers/ForeignFetchResponse.idl
similarity index 56%
copy from third_party/WebKit/Source/modules/serviceworkers/FetchEventInit.idl
copy to third_party/WebKit/Source/modules/serviceworkers/ForeignFetchResponse.idl
index 80da60fd154d6eceacead9d00b7713d0e78748f8..629bd1aabf39ff316ad82f711595736eede71b88 100644
--- a/third_party/WebKit/Source/modules/serviceworkers/FetchEventInit.idl
+++ b/third_party/WebKit/Source/modules/serviceworkers/ForeignFetchResponse.idl
@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#fetch-event-interface
+// https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#dictdef-foreignfetchevent-foreignfetchresponse
 
-dictionary FetchEventInit : ExtendableEventInit {
-  required Request request;
-  DOMString? clientId = null;
-  boolean isReload = false;
+dictionary ForeignFetchResponse {
+  required Response response;
+  USVString origin;
+  sequence<ByteString> headers;
 };