Save the history of InputMethodSubtype for reverting the subtype when IME was changed.

- Re-revert the change https://android-git.corp.google.com/g/#q,78962,n,z
*** If you want to see the diff between reverted change and new change, please see the diff between patch set 1 and the latest patch set

- TODO: Add a public function "switchToLastInputMethod"

Change-Id: Ic85d54b3b68e47a22360acaeb81202a366a34586