title: Talkback is not getting enabled through adb shell
body: <p>I've tried the command <code>adb shell settings put secure enabled_accessibility_services com.android.talkback/com.google.android.marvin.talkback.TalkBackService</code> to enable talkback from adb shell. It's toggling the ui button which signifies the status of talkback, but talkback is not actually getting enabled.
  I am trying to enable talkback programmatically for android 6.0. Is there any other way thorough which I can enable it?</p>