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

chromeos/components/tether/tether_device_state_manager.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chromeos/components/tether/tether_device_state_manager.h"
+
+#include "chromeos/network/network_state_handler.h"
+
+namespace chromeos {
+
+namespace tether {
+
+TetherDeviceStateManager::TetherDeviceStateManager(
+    NetworkStateHandler* network_state_handler)
+    : network_state_handler_(network_state_handler) {
+  network_state_handler_->AddObserver(this, FROM_HERE);
+
+  // TODO(hansberry): Set the appropriate value. For now, always set ENABLED.
+  network_state_handler_->SetTetherTechnologyState(
+      NetworkStateHandler::TechnologyState::TECHNOLOGY_ENABLED);
+}
+
+TetherDeviceStateManager::~TetherDeviceStateManager() {
+  network_state_handler_->RemoveObserver(this, FROM_HERE);
+
+  // TODO(hansberry): Determine if this should be PROHIBITED or UNAVAILABLE
+  // based on reason for shutting down.
+  network_state_handler_->SetTetherTechnologyState(
+      NetworkStateHandler::TechnologyState::TECHNOLOGY_UNAVAILABLE);
+}
+
+void TetherDeviceStateManager::DeviceListChanged() {
+  // TODO(hansberry): Implement.
+}
+
+}  // namespace tether
+
+}  // namespace chromeos