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

components/proximity_auth/proximity_monitor_impl.cc

Index: components/proximity_auth/proximity_monitor_impl.cc
diff --git a/components/proximity_auth/proximity_monitor_impl.cc b/components/proximity_auth/proximity_monitor_impl.cc
index 90821074e40f43a5aa958df48a34c6f76eaf77b9..038a17e13369a21c80ad36fc530de7a63afbb7fb 100644
--- a/components/proximity_auth/proximity_monitor_impl.cc
+++ b/components/proximity_auth/proximity_monitor_impl.cc
@@ -27,7 +27,8 @@ const int kPollingTimeoutMs = 250;
 
 // The RSSI threshold below which we consider the remote device to not be in
 // proximity.
-const int kRssiThreshold = -45;
+// Tentative value, tested between a cave and Nexus 6 device.
+const int kRssiThreshold = -50;
 
 // The weight of the most recent RSSI sample.
 const double kRssiSampleWeight = 0.3;