[EasyUnlock] Observe proximity changes and clean up TX power strategy.

components/proximity_auth/screenlock_state.h

 // Copyright 2015 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 COMPONENTS_PROXIMITY_AUTH_SCREENLOCK_STATE_H
 #define COMPONENTS_PROXIMITY_AUTH_SCREENLOCK_STATE_H
 
 namespace proximity_auth {
 
 // Possible user states of the proximity auth feature on the lock or sign-in
@@ skipping 16 matching lines @@
   // A phone eligible to unlock the local device is found, but it does not have
   // a lock screen enabled.
   PHONE_NOT_LOCKABLE,
   // An enabled phone is found, but it is not allowed to unlock the local device
   // because it does not support reporting its lock screen state.
   PHONE_UNSUPPORTED,
   // A phone eligible to unlock the local device is found, but its received
   // signal strength is too low, i.e. the phone is roughly more than 30 feet
   // away, and therefore is not allowed to unlock the device.
   RSSI_TOO_LOW,
-  // A phone eligible to unlock the local device is found, but the local
-  // device's transmission power is too high, indicating that the phone is
-  // (probably) more than 1 foot away, and therefore is not allowed to unlock
-  // the device.
-  TX_POWER_TOO_HIGH,
   // A phone eligible to unlock the local device is found; but (a) the phone is
   // locked, and (b) the local device's transmission power is too high,
   // indicating that the phone is (probably) more than 1 foot away, and
   // therefore is not allowed to unlock the device.
-  PHONE_LOCKED_AND_TX_POWER_TOO_HIGH,
+  PHONE_LOCKED_AND_RSSI_TOO_LOW,
   // The local device can be unlocked using proximity-based authentication.
   AUTHENTICATED,
 };
 
 }  // namespace proximity_auth
 
 #endif  // COMPONENTS_PROXIMITY_AUTH_SCREENLOCK_STATE_H