Provide a mechanism for the GCM driver to send message receipts to GCM.

components/gcm_driver/gcm_message_status.h

+// Copyright 2017 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.
+
+#ifndef COMPONENTS_GCM_DRIVER_GCM_MESSAGE_STATUS_H_
+#define COMPONENTS_GCM_DRIVER_GCM_MESSAGE_STATUS_H_
+
+#include "base/callback.h"
+
+namespace gcm {
+
+// Enumeration to be used for describing the status of a GCM message.
+enum class GCMMessageStatus {
+  // 0 reserved for unresolved.
+  GCM_UNRESOLVED = 0,

[Peter Beverloo, 2017/02/15 15:17:15]

Should we DCHECK that this value will never be send to the server?

[harkness, 2017/02/22 17:19:32]

Good idea. Done.

+  // 1 reserved for success.
+  GCM_SUCCESS = 1,
+
+  // 2 - 99 reserved for the GCM communication error types.
+  GCM_INVALID_SUBTYPE = 2,
+  GCM_INVALID_SENDER_ID = 3,
+  GCM_NO_REGISTRATION = 4,
+  GCM_DECRYPTION_FAILURE = 5,
+  GCM_UNKNOWN_MESSAGE_TYPE = 6,
+  GCM_INVALID_APP = 7,
+};
+
+using MessageReceiptCallback = base::Callback<void(GCMMessageStatus)>;
+
+}  // namespace gcm
+
+#endif  // COMPONENTS_GCM_DRIVER_GCM_MESSAGE_STATUS_H_