Fix extension remove tab crasher.
Fix extension remove tab crasher.

BUG=30592
TEST=See bug (includes test extension). Try also on other platforms. See further posted notes.

Review URL: http://codereview.chromium.org/554087

git-svn-id: http://src.chromium.org/svn/trunk/src@37433 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: f110b7ffe25bad94309464142e309047928d1bd9
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