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

chromeos/components/tether/tether_device_state_manager.h

Index: chromeos/components/tether/tether_device_state_manager.h
diff --git a/chromeos/components/tether/tether_device_state_manager.h b/chromeos/components/tether/tether_device_state_manager.h
new file mode 100644
index 0000000000000000000000000000000000000000..4f05e70c29c8abe644a5d2c436fc82a61eb2646f
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+++ b/chromeos/components/tether/tether_device_state_manager.h
@@ -0,0 +1,48 @@
+// 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.
+
+#ifndef CHROMEOS_COMPONENTS_TETHER_TETHER_DEVICE_STATE_MANAGER_H_
+#define CHROMEOS_COMPONENTS_TETHER_TETHER_DEVICE_STATE_MANAGER_H_
+
+#include "base/macros.h"
+#include "chromeos/network/network_state_handler.h"
+#include "chromeos/network/network_state_handler_observer.h"
+
+namespace chromeos {
+
+class NetworkStateHandler;
+
+namespace tether {
+
+// Manages the device state of tether networks. The tether state is:
+//   *TECHNOLOGY_PROHIBITED when tethering is disallowed by policy.
+//   *TECHNOLOGY_UNAVAILABLE when tethering is allowed by policy, but either
+//    the device has no Bluetooth capabilities or the logged-in user has no
+//    tether hosts associated with their account.
+//   *TECHNOLOGY_AVAILABLE when tethering is allowed by policy, the device has
+//    Bluetooth capabilities, the logged-in user has tether hosts associated
+//    with their account, but the Instant Tethering setting is disabled.
+//   *TECHNOLOGY_ENABLED when tethering is allowed by policy, the device has
+//    Bluetooth capabilities, the logged-in user has tether hosts associated
+//    with their account, and the Instant Tethering setting is enabled.
+// TODO(hansberry): Complete this class description when implemented.
+class TetherDeviceStateManager : public NetworkStateHandlerObserver {
+ public:
+  explicit TetherDeviceStateManager(NetworkStateHandler* network_state_handler);
+  ~TetherDeviceStateManager() override;
+
+  // NetworkStateHandlerObserver:
+  void DeviceListChanged() override;
+
+ private:
+  NetworkStateHandler* network_state_handler_;
+
+  DISALLOW_COPY_AND_ASSIGN(TetherDeviceStateManager);
+};
+
+}  // namespace tether
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_COMPONENTS_TETHER_TETHER_DEVICE_STATE_MANAGER_H_