[Mac/Linux] clean up the shmem file at the end of each testshell run. - Mac/Linux back shmem with a file, but the file isn't cleaned up (since it could be shared), this pulls over the same basic code we used in chrome_test_suite to clean up the files there also so they don't leak a fill up the bots.
[Mac/Linux] clean up the shmem file at the end of each testshell run.
- Mac/Linux back shmem with a file, but the file isn't cleaned up (since it could be shared), this pulls over the same basic code we used in chrome_test_suite to clean up the files there also so they don't leak a fill up the bots.

BUG=32391
TEST=nothing, http://crbug.com/36261 prevents this from really cleaning up resource leaks
Review URL: http://codereview.chromium.org/651038

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@39463 0039d316-1c4b-4281-b951-d872f2087c98

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