Fixes crash in menu code. MenuItemView doesn't handle trying to show a menu while it's already showing.
Fixes crash in menu code. MenuItemView doesn't handle trying to show a
menu while it's already showing.

BUG=90862
TEST=none
R=rhashimoto@chromium.org

Review URL: http://codereview.chromium.org/7529026

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@94752 0039d316-1c4b-4281-b951-d872f2087c98

gavinp/chromium,adobe/chromium,yitian134/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,gavinp/chromium,ropik/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,ropik/chromium,yitian134/chromium