ibus-chewing: Support IBus-1.4 API.

Manually merged a necessary part of the upstream change: https://github.com/definite/ibus-chewing/commit/d9009bf05d9d8b600936beb3c3b0ecfc84a1075a

I would rather not update ibus-chewing to tot of the upstream repository since it might make the engine unstable again.

BUG=chromium-os:9687
TEST=ran 'emerge-x86-generic ibus-chewing'

Change-Id: Iaa7b7c79eca727b51da2293c948b316efbb788a6

Review URL: http://codereview.chromium.org/5535007
3 files changed