Use tmp files in file_utils_unittests

The static file names were breaking when executing tests in parallel. This fixes it.

BUG=4138
R=andrew@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/34639004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7997 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed