Remove dcheck at CrxInstaller teardown
Remove dcheck at CrxInstaller teardown

dchecks because it tries to post a task to the file thread, but chrome is shutting down so post fails

This makes startup tests flaky.

BUG=none
TEST=startup tests do not crash, ask nsylvain.

Review URL: http://codereview.chromium.org/8438017

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@108213 0039d316-1c4b-4281-b951-d872f2087c98

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