Annotate @SystemApi with required permissions.

Most @SystemApi methods should be protected with system (or higher)
permissions, so annotate common methods with @RequiresPermission to
make automatic verification easier.

Verification is really only relevant when calling into system
services (where permissions checking can happen on the other side of
a Binder call), so annotate managers with the new @SystemService
annotation, which is now automatically documented.

This is purely a docs change; no logic changes are being made.

Test: make -j32 update-api && make -j32 offline-sdk-docs
Bug: 62263906
Change-Id: I2554227202d84465676aa4ab0dd336b5c45fc651
diff --git a/core/java/android/app/usage/NetworkStatsManager.java b/core/java/android/app/usage/NetworkStatsManager.java
index 6cd4e92..ef262e0 100644
--- a/core/java/android/app/usage/NetworkStatsManager.java
+++ b/core/java/android/app/usage/NetworkStatsManager.java
@@ -19,6 +19,7 @@
 import static com.android.internal.util.Preconditions.checkNotNull;
 
 import android.annotation.Nullable;
+import android.annotation.SystemService;
 import android.app.usage.NetworkStats.Bucket;
 import android.content.Context;
 import android.net.ConnectivityManager;
@@ -82,6 +83,7 @@
  * the above permission, even to access an app's own data usage, and carrier-privileged apps were
  * not included.
  */
+@SystemService(Context.NETWORK_STATS_SERVICE)
 public class NetworkStatsManager {
     private static final String TAG = "NetworkStatsManager";
     private static final boolean DBG = false;