Suppress uninteresting log output from mac tests due to long shim domain sockets.

The user data dir in swarmed buildbot tests typically exceeds the
maximum domain socket path length on Mac (104 characters, including the
null terminator). This generates confusing log spam in builder output.
This CL suppresses the LOG(ERROR) in MakeUnixAddrForPath() by returning
early.

BUG=240554

Review URL: https://codereview.chromium.org/27159002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229828 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229828