*   Move `layers_dense_variational_impl.py` to `layers_dense_variational.py`.

## Known Bugs

*   Using XLA:GPU with CUDA 9 and CUDA 9.1 results in garbage results and/or
    `CUDA_ILLEGAL_ADDRESS` failures.

    Google discovered in mid-December 2017 that the PTX-to-SASS compiler in CUDA
    9 and CUDA 9.1 sometimes does not properly compute the carry bit when

                            grpcStatus:
                              description: GRPC status code to use to abort the request.
                              type: string
                            http2Error:
                              type: string
                            httpStatus:
                              description: HTTP status code to use to abort the Http
                                request.

                            grpcStatus:
                              description: GRPC status code to use to abort the request.
                              type: string
                            http2Error:
                              type: string
                            httpStatus:
                              description: HTTP status code to use to abort the Http
                                request.