GitLab

Adds a unittest for the change of https://crrev.com/c/2418513 .

Also removes unnecessary "#if defined" guards.  All test cases in
allocator_shim_unittest.cc depend on USE_ALLOCATOR_SHIM, so the
entire contents of the file should be guarded with it.  Currently
it's done at:
https://source.chromium.org/chromium/chromium/src/+/master:base/BUILD.gn;drc=625ee4c0eea632fed7825725d54843ef3cd6ca2c;l=3352

Bug: 1111332
Change-Id: I2204d88b676365b317e27f21baa0fb5ba8df213c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2449869
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814133}