Hook up ProximityAuthSystem in EasyUnlockService.

components/proximity_auth/proximity_monitor.h

Index: components/proximity_auth/proximity_monitor.h
diff --git a/components/proximity_auth/proximity_monitor.h b/components/proximity_auth/proximity_monitor.h
index b3c6bd20c971809b75e2276d27e253bfbba7b2c7..b2978bf170d3ad8a792b766fab62ae155f78aec6 100644
--- a/components/proximity_auth/proximity_monitor.h
+++ b/components/proximity_auth/proximity_monitor.h
@@ -5,6 +5,8 @@
 #ifndef COMPONENTS_PROXIMITY_AUTH_PROXIMITY_MONITOR_H
 #define COMPONENTS_PROXIMITY_AUTH_PROXIMITY_MONITOR_H
 
+#include "components/proximity_auth/proximity_monitor_observer.h"
+
 namespace proximity_auth {
 
 // An interface that is responsible for tracking whether the remote device is
@@ -38,6 +40,12 @@ class ProximityMonitor {
   // Records the current proximity measurements to UMA. This should be called
   // when the user successfully authenticates using proximity auth.
   virtual void RecordProximityMetricsOnAuthSuccess() = 0;
+
+  // Adds an observer.
+  virtual void AddObserver(ProximityMonitorObserver* observer) = 0;
+
+  // Removes an observer.
+  virtual void RemoveObserver(ProximityMonitorObserver* observer) = 0;
 };
 
 }  // namespace proximity_auth