Support getting and deleting token for Instance ID.

components/gcm_driver/instance_id/instance_id.h

 // 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.
 
 #ifndef COMPONENTS_GCM_DRIVER_INSTANCE_ID_INSTANCE_ID_H_
 #define COMPONENTS_GCM_DRIVER_INSTANCE_ID_INSTANCE_ID_H_
 
 #include <map>
 #include <string>
 
@@ skipping 12 matching lines @@
 // Instance ID is managed by the InstanceIdDriver.
 class InstanceID {
  public:
   enum Result {
     // Successful operation.
     SUCCESS,
     // Invalid parameter.
     INVALID_PARAMETER,
     // Instance ID is disabled.
     DISABLED,
+    // Previous asynchronous operation is still pending to finish.
+    ASYNC_OPERATION_PENDING,
     // Network socket error.
     NETWORK_ERROR,
     // Problem at the server.
     SERVER_ERROR,
     // Other errors.
     UNKNOWN_ERROR
   };
 
   // Asynchronous callbacks.
   typedef base::Callback<void(const std::string& app_id,
@@ skipping 67 matching lines @@
  private:
   std::string app_id_;
   TokenRefreshCallback token_refresh_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(InstanceID);
 };
 
 }  // namespace instance_id
 
 #endif  // COMPONENTS_GCM_DRIVER_INSTANCE_ID_INSTANCE_ID_H_