ntp4: minor keyboard focus tweak
ntp4: minor keyboard focus tweak

don't focus the first element when the user clicks on a blank portion of the tile grid

BUG=none
TEST=clicking right next to an app shouldn't focus the first app


Review URL: http://codereview.chromium.org/8349008

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@106220 0039d316-1c4b-4281-b951-d872f2087c98

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