e>foo.cc</code>, in this case.  Such implicit dependencies
can be difficult to manage in large projects.  For that reason we
recommend the following guideline:</p>

<blockquote>
If you DEFINE a flag in <code>foo.cc</code>, either don't DECLARE it
at all, only DECLARE it in tightly related tests, or only DECLARE
it in <code>foo.h</code>.
</blockquote>

<p>You should go the do-not-DECLARE route when the flag is only needed
by <code>foo.cc</code>, and not in any other file. If you want to
modify the value of t