Add AES-ECB as a supported encryption mode in ECMG

protos/public/media_cas_encryption.proto

@@ -61,6 +61,7 @@ message CasEncryptionResponse {
     // Optional label used for the key.
     optional string track_type = 3;
     optional KeySlot key_slot = 4;
+    optional uint32 period_index = 5;
   }
   optional Status status = 1;
   optional string status_message = 2;