Support testing Direct Reply with EditTextVariations

With this CL, EditTextVariations is able to send Direct Repply
notification so that we can easily test IME behaviors there.

You don't need to set up a chat application then let it receive a
message from someone else any more just to test IME behaviors on
Direct Reply.

Fix: 122957841
Test: manually done as follows.
  1. tapas EditTextVariations
  2. make -j
  3. adb install -r \
     $ANDROID_TARGET_OUT_TESTCASES/EditTextVariations/EditTextVariations.apk
  4. Open EditTextVariations
  5. Tap the menu icon.
  6. Select "Direct Reply"
  7. Make sure that there is a Direct Reply notification.
Change-Id: Iafffcc7d138b0f502116a5e557f0c3f17e9d0b73