[Background Sync] Converting Blink code to the MVP API

Source/modules/background_sync/PeriodicSyncEventInit.idl

Index: Source/modules/background_sync/PeriodicSyncEventInit.idl
diff --git a/Source/modules/app_banner/BeforeInstallPromptEventInit.idl b/Source/modules/background_sync/PeriodicSyncEventInit.idl
similarity index 60%
copy from Source/modules/app_banner/BeforeInstallPromptEventInit.idl
copy to Source/modules/background_sync/PeriodicSyncEventInit.idl
index fc66cc8d9a905f64723a05065d055c7281fae321..60d2b728b8a9eea69f187c8524845b5210a8c763 100644
--- a/Source/modules/app_banner/BeforeInstallPromptEventInit.idl
+++ b/Source/modules/background_sync/PeriodicSyncEventInit.idl
@@ -2,6 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-dictionary BeforeInstallPromptEventInit : EventInit {
-    sequence<DOMString> platforms;
+dictionary PeriodicSyncEventInit : ExtendableEventInit {
+    required PeriodicSyncRegistration registration;
 };