Shift+Meta+Space should reverse-rotate subtypes.

This is a follow up CL to my previous CL [1], which added a new key
binding Meta+Space to rotate enabled IME subtypes.  With this CL,
Shift+Meta+Space starts reverse-rotating enabled IME subtypes as
originally planed.

 [1]: I4005692215edfcf8bed3e86b1e07000148f986f5
      ae61f711

Bug: 25753404
Bug: 28103839
Change-Id: I3694edd80be6dfe18b90360e24ae4d451b331928