Add support for GCM subtypes to desktop Instance ID implementation

components/gcm_driver/registration_info.h

Index: components/gcm_driver/registration_info.h
diff --git a/components/gcm_driver/registration_info.h b/components/gcm_driver/registration_info.h
index b9ba0a1b038c78f32ef11219796ef64f7eff4490..1ae7af4c11e5c27d3eef5256561a52fcd9897d3c 100644
--- a/components/gcm_driver/registration_info.h
+++ b/components/gcm_driver/registration_info.h
@@ -104,8 +104,14 @@ struct InstanceIDTokenInfo : public RegistrationInfo {
   // E.g. for sending GCM messages, 'GCM' scope should be used.
   std::string scope;
 
+  // Whether to send |app_id| to GCM as the "subtype" field (supported on all
+  // platforms) or as the "category" field (not supported on Android, since
+  // Google Play Services always sends the app package name as "category").
+  bool use_subtype;
+
   // Allows including a small number of string key/value pairs that will be
-  // associated with the token and may be used in processing the request.
+  // associated with the token and may be used in processing the request. These
+  // are not serialized/deserialized!
   std::map<std::string, std::string> options;
 };