Add a UsbModemSwitcher class.

This CL adds a UsbModemSwitcher class, which monitors when a supported
USB device is added to the system and initiates a modem switch operation
on the device.

BUG=chromium:249487
TEST=Build and run unit tests.

Change-Id: If8920936d015b2e63473ee029974c03510e7264e
Reviewed-on: https://gerrit.chromium.org/gerrit/58666
Commit-Queue: Ben Chan <benchan@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
2 files changed