Use a non-deprecated method to get a string from an OSStatus error.

The functions GetMacOSStatusErrorString() and GetMacOSStatusCommentString() have
been deprecated since OSX 10.8. The official replacement is NSError.

BUG=547071

Review URL: https://codereview.chromium.org/1753523002

Cr-Commit-Position: refs/heads/master@{#378564}
7 files changed