Fix mobile data preferred on multi-user devices.

The mobile data preferred feature stores the list of UIDs in
Settings.Secure, which is per-user. But the code only sets, reads
and observes the setting for the current user instead of for all
users. This does not work on HSUM or automotive.

Fix this as follows:
- Register the ContentObserver on UserHandle.ALL
- Any time the observer fires, read the setting on all current
  users, and operate on the merged result.
- Ensure that the code gets called on ACTION_USER_ADDED and
  ACTION_USER_REMOVED.

Because the code now aggregates the setting for all UIDs, it
should just work on single-user devices. It should also work if
there are OEM devices that store all UIDs (for all users) in
Settings.Secure for user 0.

Because the bug is fixed, re-enable the test on automotive.

Also fix style nits.

Fix: 404186833
Flag: EXEMPT bug fix
Test: covered by existing CTS tests
Change-Id: I69ad789f1c7c7f3bab04ab8789dfb93ee0de553d

service/src/com/android/server/ConnectivityService.java

@@ -2516,7 +2516,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 EVENT_CONFIGURE_ALWAYS_ON_NETWORKS);
 
         // Watch for mobile data preferred uids changes.
-        mSettingsObserver.observe(
+        mSettingsObserver.observeForAllUsers(
                 Settings.Secure.getUriFor(ConnectivitySettingsManager.MOBILE_DATA_PREFERRED_UIDS),
                 EVENT_MOBILE_DATA_PREFERRED_UIDS_CHANGED);
 
@@ -4388,7 +4388,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
         // Note that updating can be skipped here if the list is empty only because no uid
         // rules are applied before system ready. Normally, the empty uid list means to clear
         // the uids rules on netd.
-        if (!ConnectivitySettingsManager.getMobileDataPreferredUids(mContext).isEmpty()) {
+        if (!getMobileDataPreferredUids().isEmpty()) {
             mHandler.sendEmptyMessage(EVENT_MOBILE_DATA_PREFERRED_UIDS_CHANGED);
         }
 
@@ -14971,8 +14971,17 @@ public class ConnectivityService extends IConnectivityManager.Stub
         return requests;
     }
 
+    private Set<Integer> getMobileDataPreferredUids() {
+        Set<Integer> uids = new ArraySet<>();
+        for (UserHandle userHandle : mUserManager.getUserHandles(/* excludeDying= */ true)) {
+            final Context userContext = mContext.createContextAsUser(userHandle, 0 /* flags */);
+            uids.addAll(ConnectivitySettingsManager.getMobileDataPreferredUids(userContext));
+        }
+        return uids;
+    }
+
     private void handleMobileDataPreferredUidsChanged() {
-        mMobileDataPreferredUids = ConnectivitySettingsManager.getMobileDataPreferredUids(mContext);
+        mMobileDataPreferredUids = getMobileDataPreferredUids();
         removeDefaultNetworkRequestsForPreference(PREFERENCE_ORDER_MOBILE_DATA_PREFERERRED);
         addPerAppDefaultNetworkRequests(
                 createNrisFromMobileDataPreferredUids(mMobileDataPreferredUids));