Add IDL and initial Blink API for Background Sync

Source/modules/background_sync/SyncRegistrationOptions.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// https://w3c.github.io/encrypted-media/#idl-def-MediaKeyStatusMap
-
-enum MediaKeyStatus {
-    "usable",
-    "expired",
-    "output-not-allowed",
-    "internal-error"
+enum SyncNetworkType {
+  "network-any",
+  "network-offline",
+  "network-online",
+  "network-non-mobile",
 };
 
 [
-    GarbageCollected,
-] interface MediaKeyStatusMap {
-    readonly attribute unsigned long size;
-    readonly maplike <BufferSource, MediaKeyStatus>;
+    RuntimeEnabled=BackgroundSync,
+] dictionary SyncRegistrationOptions {
+    SyncNetworkType minRequiredNetwork = "network-online";
+    boolean allowOnBattery = true;
+    boolean idleRequired = false;
 };