This CL watches a change to Settings.Secure.ENABLED_INPUT_METHODS and updates search index of IMEs. Bug: 32643633 Test: After installing AOSP LatinIME.apk, enabling/disabling the IME and searching "AOSP", then verify the search landing page is correct depending on the IME's enabling state. Test: Update robolectric test. Change-Id: I85fa845238b89375e56b207a014af6432f9db647