Handle removed UIDs in network stats and policy.

When UID_REMOVED, clean up any existing UID network policy so it
doesn't linger for future apps.  Also move any NetworkStatsHistory
to special UID_REMOVED tracking bucket.

Tests for new removal code.  Also test detailed UID stats, including
network changes to verify template matching logic.

Bug: 4584212
Change-Id: I9faadf6b6f3830eb45d86c7f1980a27cdbcdb11e

core/java/android/net/NetworkIdentity.java

@@ -95,9 +95,13 @@ public class NetworkIdentity {
 
         final String subscriberId;
         if (isNetworkTypeMobile(type)) {
-            final TelephonyManager telephony = (TelephonyManager) context.getSystemService(
-                    Context.TELEPHONY_SERVICE);
-            subscriberId = telephony.getSubscriberId();
+            if (state.subscriberId != null) {
+                subscriberId = state.subscriberId;
+            } else {
+                final TelephonyManager telephony = (TelephonyManager) context.getSystemService(
+                        Context.TELEPHONY_SERVICE);
+                subscriberId = telephony.getSubscriberId();
+            }
         } else {
             subscriberId = null;
         }

core/java/android/net/TrafficStats.java

@@ -41,6 +41,14 @@ public class TrafficStats {
      */
     public final static int UNSUPPORTED = -1;
 
+    /**
+     * Special UID value used when collecting {@link NetworkStatsHistory} for
+     * removed applications.
+     *
+     * @hide
+     */
+    public static final int UID_REMOVED = -4;
+
     /**
      * Snapshot of {@link NetworkStats} when the currently active profiling
      * session started, or {@code null} if no session active.