Fix rebuilding the profile selector on the OSX App Launcher.

rebuildMenu was only rebuilding the NSMenu, not the menu Model. Do both.

Also add tests, and remove the unused AppListMenu::CURRENT_USER, to fix
a broken test related to the test not observing the user model properly.

BUG=302882
TEST=Open the App Launcher on OSX. Go to chrome://settings and add a
user. The new user should appear in the App Lanucher profile selctor.

Review URL: https://codereview.chromium.org/25535006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226435 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226435