Support getting and deleting token for Instance ID.

components/gcm_driver/instance_id/instance_id.h

Index: components/gcm_driver/instance_id/instance_id.h
diff --git a/components/gcm_driver/instance_id/instance_id.h b/components/gcm_driver/instance_id/instance_id.h
index 8141a3a5c028b75218b532e8d8eb7883a32b74f9..343b9c5e72c499ebb7f48eb941d73de923bd992d 100644
--- a/components/gcm_driver/instance_id/instance_id.h
+++ b/components/gcm_driver/instance_id/instance_id.h
@@ -30,6 +30,8 @@ class InstanceID {
     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.