Add input device setting APIs to autotestPrivate

The CL adds APIs in autotestPrivate so that one can set input
device settings from an autotest. These settings appears as
touchpad/mouse related settings in the user preference page.

Contributed by [email protected]

BUG=434471,400022
TEST=Manual

Review URL: https://codereview.chromium.org/764273002

Cr-Commit-Position: refs/heads/master@{#306785}
7 files changed