Remove unnecessary const (causes compile error on Mac)

R=darin@chromium.org
TBR=darin@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/46973006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232720 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232720