[mac] Allow the OSX App Launcher menu to be invalidated.

[mac] Allow the OSX App Launcher menu to be invalidated.

Currently the app launcher will show the old profile name, and no login
identity, after signing in for the first time, until the browser is
restarted (or the app list profile is switched).

This CL allows the app list menu to be invalidated when the signin
status changes. Simply setting the CURRENT_USER menu item to be
'dynamic' is insufficient, because the menu item uses a custom view
which needs to be released and re-appended.

BUG=262639
TEST=Have Chrome not signed in, open a browser. Open app launcher, see
signin page, and sign in, leave browser window open. Reopen app
launcher, open menu: it should show email of the just-signed-in user.

Review URL: https://chromiumcodereview.appspot.com/22424007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@216651 0039d316-1c4b-4281-b951-d872f2087c98