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

chromeos/network/tether_constants.h

Index: chromeos/network/tether_constants.h
diff --git a/chromeos/network/tether_constants.h b/chromeos/network/tether_constants.h
index 26b4f21d43cf086f2078649b2fc90da2304597d0..4d73d1dbf28d5ae7c65646cec1b7ae9cf6518537 100644
--- a/chromeos/network/tether_constants.h
+++ b/chromeos/network/tether_constants.h
@@ -22,6 +22,12 @@ CHROMEOS_EXPORT extern const char kTetherBatteryPercentage[];
 CHROMEOS_EXPORT extern const char kTetherCarrier[];
 CHROMEOS_EXPORT extern const char kTetherSignalStrength[];
 
+// The device path used for the tether DeviceState.
+CHROMEOS_EXPORT extern const char kTetherDevicePath[];
+
+// The name used for the tether DeviceState.
+CHROMEOS_EXPORT extern const char kTetherDeviceName[];
+
 }  // namespace chromeos
 
 #endif  // CHROMEOS_NETWORK_TETHER_CONSTANTS_H_