Fixes crash in Browser::AddTabWithURL. The crash would happen if GetOrCreateTabbedBrowser returned this.
Fixes crash in Browser::AddTabWithURL. The crash would happen if
GetOrCreateTabbedBrowser returned this.

BUG=42914
TEST=see bug

Review URL: http://codereview.chromium.org/1812009

git-svn-id: http://src.chromium.org/svn/trunk/src@46263 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 1f45e5fa3af87ce6f2b52b6df1803d7791a91898
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