mac: Fix a -Wobjc-redundant-literal-use warning
mac: Fix a -Wobjc-redundant-literal-use warning

BUG=none
TEST=none
TBR=rsesek

Review URL: http://codereview.chromium.org/9706027

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@126722 0039d316-1c4b-4281-b951-d872f2087c98

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