code: public com.google.protobuf.ByteString
        getVisibleDeviceListBytes() {
      java.lang.Object ref = visibleDeviceList_;
      if (ref instanceof java.lang.String) {
        com.google.protobuf.ByteString b = 
            com.google.protobuf.ByteString.copyFromUtf8(
                (java.lang.String) ref);
        visibleDeviceList_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
docs: <pre>
  A comma-separated list of GPU ids that determines the 'visible'
  to 'virtual' mapping of GPU devices.  For example, if TensorFlow
  can see 8 GPU devices in the process, and one wanted to map
  visible GPU devices 5 and 3 as "/gpu:0", and "/gpu:1", then one
  would specify this field as "5,3".  This field is similar in
  spirit to the CUDA_VISIBLE_DEVICES environment variable, except
  it applies to the visible GPU devices in the process.
  NOTE: The GPU driver provides the process with the visible GPUs
  in an order which is not guaranteed to have any correlation to
  the *physical* GPU id in the machine.  This field is used for
  remapping "visible" to "virtual", which means this operates only
  after the process starts.  Users are required to use vendor
  specific mechanisms (e.g., CUDA_VISIBLE_DEVICES) to control the
  physical to visible device mapping prior to invoking TensorFlow.
  </pre>
  
  <code>optional string visible_device_list = 5;</code>