system_api: Add GenerateVirtualFileId and OpenFileById to VirtualFileProvider

BUG=b:158606367
TEST=builds

Change-Id: I01de7e658ac193384b7bd030f20e191fc3f60c0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2444617
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Tested-by: Cherie Cheung <cherieccy@chromium.org>
Commit-Queue: Cherie Cheung <cherieccy@chromium.org>
diff --git a/system_api/dbus/service_constants.h b/system_api/dbus/service_constants.h
index 025ce29..cd33044 100644
--- a/system_api/dbus/service_constants.h
+++ b/system_api/dbus/service_constants.h
@@ -540,7 +540,9 @@
 constexpr char kVirtualFileProviderInterface[] =
     "org.chromium.VirtualFileProvider";
 // Methods
+constexpr char kGenerateVirtualFileIdMethod[] = "GenerateVirtualFileId";
 constexpr char kOpenFileMethod[] = "OpenFile";
+constexpr char kOpenFileByIdMethod[] = "OpenFileById";
 }  // namespace virtual_file_provider
 
 namespace crosdns {