Plumb environment variable into test case.
Plumb environment variable into test case.

This had been added in a previous commit, but wasn't fully wired up since it
requires a recent version of Bazel.

PiperOrigin-RevId: 366850311
Change-Id: I399849c1d95b7716b97ef8896510e2d7d3438ed8

google/tcmalloc,google/tcmalloc,google/tcmalloc