Add additional overriding methods to signature files

This change adds overriding methods that are essential to compile the
stubs generated from the signature files.

More information and the background for this change is available at
go/add-overriding-one-pager.

Test: m checkapi
Bug: 299366704
Change-Id: Idba307148fd9afa87bfb7e0c89e00d9bd97ec204
diff --git a/framework-t/api/system-current.txt b/framework-t/api/system-current.txt
index 9bdb595..f6b5657 100644
--- a/framework-t/api/system-current.txt
+++ b/framework-t/api/system-current.txt
@@ -1,6 +1,4 @@
 // Signature format: 2.0
-// - add-additional-overrides=no
-// - migrating=Migration in progress see b/299366704
 package android.app.usage {
 
   public class NetworkStatsManager {
@@ -307,6 +305,7 @@
     ctor public NetworkStats(long, int);
     method @NonNull public android.net.NetworkStats add(@NonNull android.net.NetworkStats);
     method @NonNull public android.net.NetworkStats addEntry(@NonNull android.net.NetworkStats.Entry);
+    method public android.net.NetworkStats clone();
     method public int describeContents();
     method @NonNull public java.util.Iterator<android.net.NetworkStats.Entry> iterator();
     method @NonNull public android.net.NetworkStats subtract(@NonNull android.net.NetworkStats);