Fix warnings on Mac that has been reported by Eric. "warning: 'cloud_print::PrintSystemCUPS' has a field 'cloud_print::PrintSystemCUPS::printer_map_' whose type uses the anonymous namespace"
Fix warnings on Mac that has been reported by Eric.
"warning: 'cloud_print::PrintSystemCUPS' has a field
'cloud_print::PrintSystemCUPS::printer_map_' whose type uses the
anonymous namespace"

For some reasons my machine did not produce such warnings and
print_system_cups.cc compiled just fine.

Eric, Could you please verify this fixes the issue?

BUG=none
TEST=Verify no warnings produced on Mac

Review URL: http://codereview.chromium.org/4632004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@65829 0039d316-1c4b-4281-b951-d872f2087c98

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