[Mac] Make profile-locking error the same as failing to lock.
[Mac] Make profile-locking error the same as failing to lock.

Previously, the profile-locking code was conservative in the face of
errors.  Histograms indicate that the error rate is acceptable (no
errors seen), so flip locking errors to me failure-to-lock.

BUG=58986
TEST=none

Review URL: http://codereview.chromium.org/5717002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@68871 0039d316-1c4b-4281-b951-d872f2087c98

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