These `GoogleCrashdumpUploader` instances need to be cleaned up; place
them on the stack.
Doing this unmasks another bug in this code: the `MockLibcurlWrapper`
instance we're passing into these `GoogleCrashdumpUploader`s becomes
owned by the `GoogleCrashdumpUploader` in question. Putting them on the
stack makes `free()` unhappy when the `GoogleCrashdumpUploader` they're
given to gets destructed.
Bug: b:235999011
Change-Id: I5d0424a1c09d32ea34a8fa6f5e52d3695ee6e857
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3756172
Reviewed-by: Mike Frysinger <vapier@chromium.org>
