Fixes bug in MainMenu that if there are no browsers around when timer fires we get a crash.
Fixes bug in MainMenu that if there are no browsers around when timer
fires we get a crash.

BUG=none
TEST=none
TBR=oshima

Review URL: http://codereview.chromium.org/502065

git-svn-id: http://src.chromium.org/svn/trunk/src@34905 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: dda6333e8cc09191d001fc98ab4e089f32d459e9
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