message: Populate FunctionLibraryRuntime::Options::step_container
  I found this when prototyping a speculative idea which may or may not eventually
  land; splitting this out separately since it looks like an obvious omission.
diff: @@ -120,6 +120,7 @@ void SetRunOptions(OpKernelContext* ctx, FunctionLibraryRuntime::Options* opts,
  opts->stats_collector = ctx->stats_collector();
  }
  opts->runner = ctx->runner();
  + opts->step_container = ctx->step_container();
  }
  class IfOp : public AsyncOpKernel {
  