Tests that need to be addressed:

KeepAliveOperationTest
KeepAliveSchedulerTest
HostScannerOperationTest
HostScannerImplTest
TetherConnectorImplTest
ConnectTetheringOperationTest
DisconnectTetheringOperationTest
HostConnectionMetricsLoggerTest
DisconnectTetheringRequestSenderTest
ConnectTetheringRequestSenderTest

As far as I can tell, these will fail as-is once the kMultiDeviceApi flag is enabled because they do not fully initialize their FakeDeviceSyncClient and FakeSecureChannelClient objects. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a73bb31594cd5e2aa64817f803ec057d0badcaa6

commit a73bb31594cd5e2aa64817f803ec057d0badcaa6
Author: Regan Hsu <hsuregan@chromium.org>
Date: Thu Nov 15 19:29:57 2018

[CrOS MultiDevice] Remove MessageTransferOperation kMultiDeviceApi references.

We are launching the new multi-device services and removing
the old functionality.  As part of the internal cleanup, we
are removing references to kMultiDeviceApi from
MessageTransferOperation - as the functionality it entails
will become the default action - and removing code that
relies on old methods.

Many of the tests that rely on fake classes that mimic old
functionality fail.  As a result, this CL disables those tests.

Bug: 905151

Change-Id: I9ad4572431afe9e659e1a82edf878b09d3734367
Reviewed-on: https://chromium-review.googlesource.com/c/1328163
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608474}
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/connect_tethering_operation_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/disconnect_tethering_operation_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/disconnect_tethering_request_sender_impl_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/host_scanner_impl_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/host_scanner_operation_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/keep_alive_operation_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/keep_alive_scheduler_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/message_transfer_operation.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/message_transfer_operation.h
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/message_transfer_operation_unittest.cc
[modify] https://crrev.com/a73bb31594cd5e2aa64817f803ec057d0badcaa6/chromeos/components/tether/tether_connector_impl_unittest.cc