Add Mojo types and service definitions for Background Sync API

content/public/common/background_sync.mojom

+// 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.
+
+module content;
+
+enum BackgroundSyncNetworkState {
+  ANY,
+  AVOID_CELLULAR,
+  ONLINE,
+  MAX=ONLINE
+};
+
+enum BackgroundSyncPowerState {
+  AUTO,
+  AVOID_DRAINING,
+  MAX=AVOID_DRAINING
+};
+
+enum BackgroundSyncPeriodicity {
+  PERIODIC,
+  ONE_SHOT,
+  MAX=ONE_SHOT
+};
+
+struct SyncRegistration {
+  int64 id = -1;
+  BackgroundSyncPeriodicity periodicity = ONE_SHOT;
+  string tag = "";
+  uint64 min_period_ms = 0;
+  BackgroundSyncNetworkState network_state = ONLINE;
+  BackgroundSyncPowerState power_state = AUTO;
+};