Add the NotificationDatabaseData structure and protobuf

content/browser/notifications/notification_database_data.proto

+// 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.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package content;
+
+// Stores information about a Web Notification. This message is the protocol
+// buffer meant to serialize the content::NotificationDatabaseData structure.
+//
+// Next tag: 5
+message NotificationDatabaseDataProto {
+  optional int64 notification_id = 1;
+
+  optional string origin = 2;
+  optional int64 service_worker_registration_id = 3;
+
+  // Actual data payload of the notification. This message is the protocol
+  // buffer meant to serialize the content::PlatformNotificationData structure.
+  //
+  // Next tag: 8
+  message NotificationData {
+    enum Direction {
+      LEFT_TO_RIGHT = 0;
+      RIGHT_TO_LEFT = 1;
+    }
+
+    optional string title = 1;
+    optional Direction direction = 2;
+    optional string lang = 3;
+    optional string body = 4;
+    optional string tag = 5;
+    optional string icon = 6;
+    optional bool silent = 7;
+  }
+
+  optional NotificationData notification_data = 4;
+}