Add autoclick menu item to ash accessibility system tray.

BUG=272401
TEST=updated browser_tests

Review URL: https://codereview.chromium.org/27238008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230498 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230498