Add a minor text member to ui::MenuModel.
The menu model currently has a |sublabel| member which is does not match
the documentation. This CL implements the documented behavior for
|sublabel| and migrates the previous functionality into a new member
|minor_text|.
The new sublabel functionality is required for the app list profile
selector in https://chromiumcodereview.appspot.com/
20656002/.
BUG=254143
TEST=No functional changes.
Review URL: https://chromiumcodereview.appspot.com/
23536002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221131 0039d316-1c4b-4281-b951-d872f2087c98