Remove TabContents from TabStripModelObserver::TabDetachedAt.

BUG=107201
TEST=no visible change


Review URL: https://chromiumcodereview.appspot.com/11293205

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@167122 0039d316-1c4b-4281-b951-d872f2087c98
ExtensionUnloadNotificationObserver::ExtensionUnloadNotificationObserver()
    : did_receive_unload_notification_(false) {
  registrar_.Add(this, chrome::NOTIFICATION_EXTENSION_UNLOADED,
                 content::NotificationService::AllSources());
}

ExtensionUnloadNotificationObserver::ExtensionUnloadNotificationObserver()
    : did_receive_unload_notification_(false) {
  registrar_.Add(this, chrome::NOTIFICATION_EXTENSION_UNLOADED,
                 content::NotificationService::AllSources());
}
