[CrOS Tether] Add the notion of a tether DeviceState.

chromeos/components/tether/active_host_network_state_updater_unittest.cc

Index: chromeos/components/tether/active_host_network_state_updater_unittest.cc
diff --git a/chromeos/components/tether/active_host_network_state_updater_unittest.cc b/chromeos/components/tether/active_host_network_state_updater_unittest.cc
index 2acf577d0f9b39d1379b70b1c0be57c70fd92d86..57e95e512d773041db5cc12a30029ff610a2037d 100644
--- a/chromeos/components/tether/active_host_network_state_updater_unittest.cc
+++ b/chromeos/components/tether/active_host_network_state_updater_unittest.cc
@@ -47,6 +47,8 @@ class ActiveHostNetworkStateUpdaterTest : public NetworkStateTest {
   void SetUp() override {
     DBusThreadManager::Initialize();
     NetworkStateTest::SetUp();
+    network_state_handler()->SetTetherTechnologyState(
+        NetworkStateHandler::TECHNOLOGY_ENABLED);
     SetUpTetherNetwork();
     SetUpWifiNetwork();