Allocate well-known tag for app store updates.

This way an app store can shift blame for update-related network
traffic onto the app that is being updated.

Using a well-known tag makes it easy for developers to identify
that they didn't explicitly request the traffic at runtime, similar
to how backup/restore traffic is handled.

Bug: 38282350
Test: builds, boots
Change-Id: I003dd7c9615d4ab318250f1e44fa5d195ac94d23
diff --git a/core/java/android/net/TrafficStats.java b/core/java/android/net/TrafficStats.java
index f934616..1985707 100644
--- a/core/java/android/net/TrafficStats.java
+++ b/core/java/android/net/TrafficStats.java
@@ -109,25 +109,26 @@
      */
     public static final int TAG_SYSTEM_RESTORE = 0xFFFFFF04;
 
-    /** @hide */
-    public static final int TAG_SYSTEM_DHCP = 0xFFFFFF05;
-    /** @hide */
-    public static final int TAG_SYSTEM_NTP = 0xFFFFFF06;
-    /** @hide */
-    public static final int TAG_SYSTEM_PROBE = 0xFFFFFF07;
-    /** @hide */
-    public static final int TAG_SYSTEM_NEIGHBOR = 0xFFFFFF08;
-    /** @hide */
-    public static final int TAG_SYSTEM_GPS = 0xFFFFFF09;
-    /** @hide */
-    public static final int TAG_SYSTEM_PAC = 0xFFFFFF0A;
-
     /**
-     * Sockets that are strictly local on device; never hits network.
+     * Default tag value for code or resources downloaded by an app store on
+     * behalf of the app, such as app updates.
      *
      * @hide
      */
-    public static final int TAG_SYSTEM_LOCAL = 0xFFFFFFAA;
+    public static final int TAG_SYSTEM_CODE = 0xFFFFFF05;
+
+    /** @hide */
+    public static final int TAG_SYSTEM_DHCP = 0xFFFFFF40;
+    /** @hide */
+    public static final int TAG_SYSTEM_NTP = 0xFFFFFF41;
+    /** @hide */
+    public static final int TAG_SYSTEM_PROBE = 0xFFFFFF42;
+    /** @hide */
+    public static final int TAG_SYSTEM_NEIGHBOR = 0xFFFFFF43;
+    /** @hide */
+    public static final int TAG_SYSTEM_GPS = 0xFFFFFF44;
+    /** @hide */
+    public static final int TAG_SYSTEM_PAC = 0xFFFFFF45;
 
     private static INetworkStatsService sStatsService;
 
@@ -210,6 +211,19 @@
     }
 
     /**
+     * Set active tag to use when accounting {@link Socket} traffic originating
+     * from the current thread. The tag used internally is well-defined to
+     * distinguish all code-related traffic, such as updates performed by an app
+     * store.
+     *
+     * @hide
+     */
+    @SystemApi
+    public static void setThreadStatsTagCode() {
+        setThreadStatsTag(TAG_SYSTEM_CODE);
+    }
+
+    /**
      * Get the active tag used when accounting {@link Socket} traffic originating
      * from the current thread. Only one active tag per thread is supported.
      * {@link #tagSocket(Socket)}.