Add one more cast to placate the 10.6 SDK.
Add one more cast to placate the 10.6 SDK.

BUG=none
TEST=none
Review URL: http://codereview.chromium.org/543158

git-svn-id: http://src.chromium.org/svn/trunk/src@36892 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: a7a92a6e86c7e00c5e04442729f7504f88b70aba
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser