Elim spurious override in system_tray.cc.
Elim spurious override in system_tray.cc.

Win fix for CL: http://codereview.chromium.org/10235010/

TBR=sadrul
BUG=124269
TEST=win aura compiles

Review URL: https://chromiumcodereview.appspot.com/10269015

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@134616 0039d316-1c4b-4281-b951-d872f2087c98

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