Use event init dictionaries in modules/{notifications,push_messaging,serviceworkers}

Source/modules/serviceworkers/InstallEventInit.idl

Index: Source/modules/serviceworkers/InstallEventInit.idl
diff --git a/Source/modules/serviceworkers/RegistrationOptions.idl b/Source/modules/serviceworkers/InstallEventInit.idl
similarity index 58%
copy from Source/modules/serviceworkers/RegistrationOptions.idl
copy to Source/modules/serviceworkers/InstallEventInit.idl
index cdeda388e49264bc8737fdee2b8e7aea4655688b..16bb318439ceb4ae6a1608beee2215caac7957f4 100644
--- a/Source/modules/serviceworkers/RegistrationOptions.idl
+++ b/Source/modules/serviceworkers/InstallEventInit.idl
@@ -2,7 +2,9 @@
 // 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#registration-option-list-dictionary
-dictionary RegistrationOptions {
-    USVString scope = "/";
+// https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#install-event-interface
+
+dictionary InstallEventInit : ExtendableEventInit {
+    // FIXME: add following member.
+    // ServiceWorker activeWorker;
 };