[Android] Implement bridge for password accessory

This CL adds the JNI classes to wire the communication between
native code and UI code of the password-specific accessory.

Testing is not really possible:
1. On the native side, verifying interacting with the UI isn't
really doable (esp. because this CL makes no UI changes yet).
2. On the UI-side, we don't currently have a way to set up a
synced profile to save and provide passwords.

I am open to any good idea which extends the integration
tests in the follow-up CL.

Bug: 811747, 845458
Change-Id: I10775bb92d576bcaab0f9c998d64f3377a713707
Reviewed-on: https://chromium-review.googlesource.com/1068671
Reviewed-by: Vasilii Sukhanov <[email protected]>
Reviewed-by: Bernhard Bauer <[email protected]>
Commit-Queue: Friedrich Horschig <[email protected]>
Cr-Commit-Position: refs/heads/master@{#564520}
11 files changed