Implement ArcInputMethodManagerService::SwitchImeTo().

This CL adds a new method, |SwitchImeTo()|, to
ArcInputMethodManagerService.
ArcInputMethodManagerService observes the change of the active IME in
Chrome OS and send the change to Arc container to synchronize the state
between Chrome OS's InputMethodManager and Arc's InputMethodManager.

Bug: 845079
Test: unit_tests
Change-Id: Ib76795c9c768504a50ec3c4683c5ace6801aaf1d
Reviewed-on: https://chromium-review.googlesource.com/1102230
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567941}
3 files changed