How to write additional content into bbl file?

Question

How can I tell LaTeX to write additional content to bbl file?

Background of my question (see also MWE below): The page number for the bibliography displayed in the table of contents is correct if and only if \addcontentsline{toc}{chapter}{Bibliography} is placed at the beginning of the thebibliography environment. Hence, using bibTeX I need to write \addcontentsline{toc}{chapter}{Bibliography} into the bbl file. If I place it before \begin{thebibliography} the page number is first page of bibliography - 1, if I place it after \end{thebibliography} it is last page of bibliography + 1 (which in the MWE would be correct but not in general).

\documentclass{book}

\begin{document}
\tableofcontents

\begin{thebibliography}{B}
\addcontentsline{toc}{chapter}{Bibliography}
\bibitem[B]{B}
A. Brown
\newblock {\em Mathematics}.
\end{thebibliography}

\end{document}

Answer 1

The correct approach to add a bibliography entry to the ToC is not to fiddle with the .bbl file, but a) to add \addcontentsline{toc}{(sectioning level>}{Bibliography} to the (class-dependend!) definition of the thebibliography environment or b) to load packages for this task, e.g., \usepackage[nottoc]{tocbibind}.

See also Bibliography in table of contents; Gonzalo Medina's answer shows how to patch the thebibliography environment for the book class.