message: comment about the "gpu" platform
diff: @@ -60,6 +60,7 @@ xla::StatusOr<xla::DeviceAssignment> GpuClient::GetDefaultDeviceAssignment(
  // Builds an xla::LocalClient for the GPU platform.
  StatusOr<LocalClient*> GetGpuXlaClient() {
  + // "gpu" will be substitued by the default defined in platform_util.cc
  TF_ASSIGN_OR_RETURN(se::Platform * platform,
  PlatformUtil::GetPlatform("gpu"));
  if (platform->VisibleDeviceCount() <= 0) {
  