Adds registerSessionListener API to Log

Adds the registerSessionListener API to android.telecom.Log to allow
callbacks to occur when a session has been fully completed.
CP from internal branch.

Test: Manual Testing
Bug: 26571395
Change-Id: I70ebd6f432768a5d7bd8f3a0997b8e0ef335bb35
diff --git a/telecomm/java/android/telecom/Log.java b/telecomm/java/android/telecom/Log.java
index ecda3cd..01af76b 100644
--- a/telecomm/java/android/telecom/Log.java
+++ b/telecomm/java/android/telecom/Log.java
@@ -199,6 +199,10 @@
         getSessionManager().endSession();
     }
 
+    public static void registerSessionListener(SessionManager.ISessionListener l) {
+        getSessionManager().registerSessionListener(l);
+    }
+
     public static String getSessionId() {
         // If the Session logger has not been initialized, then there have been no sessions logged.
         // Don't load it now!