[MS63.1] Remove TrafficStats.TAG_SYSTEM_DOWNLOAD dependency

Replace with system Api.

Test: TH
Bug: 204830222
CTS-Coverage-Bug: 215043101
Change-Id: Ic14b26d2862f6fe8bee18fe0c9eaf183052452ee
diff --git a/framework-t/src/android/net/TrafficStats.java b/framework-t/src/android/net/TrafficStats.java
index 032bc3f..1af32bf 100644
--- a/framework-t/src/android/net/TrafficStats.java
+++ b/framework-t/src/android/net/TrafficStats.java
@@ -282,6 +282,18 @@
     }
 
     /**
+     * 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 download provider traffic.
+     *
+     * @hide
+     */
+    @SystemApi
+    public static void setThreadStatsTagDownload() {
+        setThreadStatsTag(TAG_SYSTEM_DOWNLOAD);
+    }
+
+    /**
      * 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)}.