Add feature flag for "no data" backup calls

This will allow us to turn off the new functionality while the
transport implementations are updated.

Bug: 147481066
Test: m -j RunBackupFrameworksServicesRoboTests
Change-Id: I8c0019ff80d94dd8d94299a7b03b78e3081f2b8e

core/java/android/util/FeatureFlagUtils.java

@@ -44,6 +44,9 @@ public class FeatureFlagUtils {
     public static final String SETTINGS_FUSE_FLAG = "settings_fuse";
     public static final String NOTIF_CONVO_BYPASS_SHORTCUT_REQ =
             "settings_notif_convo_bypass_shortcut_req";
+    /** @hide */
+    public static final String BACKUP_NO_KV_DATA_CHANGE_CALLS =
+            "backup_enable_no_data_notification_calls";
 
     private static final Map<String, String> DEFAULT_FLAGS;
 
@@ -62,6 +65,9 @@ public class FeatureFlagUtils {
         DEFAULT_FLAGS.put("settings_controller_loading_enhancement", "false");
         DEFAULT_FLAGS.put("settings_conditionals", "false");
         DEFAULT_FLAGS.put(NOTIF_CONVO_BYPASS_SHORTCUT_REQ, "true");
+
+        // Disabled until backup transports support it.
+        DEFAULT_FLAGS.put(BACKUP_NO_KV_DATA_CHANGE_CALLS, "false");
     }
 
     /**

services/backup/java/com/android/server/backup/keyvalue/KeyValueBackupTask.java

@@ -47,6 +47,7 @@ import android.os.RemoteException;
 import android.os.SELinux;
 import android.os.UserHandle;
 import android.os.WorkSource;
+import android.util.FeatureFlagUtils;
 import android.util.Log;
 
 import com.android.internal.annotations.GuardedBy;
@@ -399,6 +400,12 @@ public class KeyValueBackupTask implements BackupRestoreTask, Runnable {
      *                     the transport have no data.
      */
     private void informTransportOfUnchangedApps(Set<String> appsBackedUp) {
+        // If the feautre is not enabled then we just exit early.
+        if (!FeatureFlagUtils.isEnabled(mBackupManagerService.getContext(),
+                FeatureFlagUtils.BACKUP_NO_KV_DATA_CHANGE_CALLS)) {
+            return;
+        }
+
         String[] succeedingPackages = getSucceedingPackages();
         if (succeedingPackages == null) {
             // Nothing is succeeding, so end early.

services/robotests/backup/src/com/android/server/backup/keyvalue/KeyValueBackupTaskTest.java

@@ -96,6 +96,7 @@ import android.os.Message;
 import android.os.ParcelFileDescriptor;
 import android.os.RemoteException;
 import android.platform.test.annotations.Presubmit;
+import android.util.FeatureFlagUtils;
 import android.util.Pair;
 
 import com.android.internal.backup.IBackupTransport;
@@ -258,6 +259,9 @@ public class KeyValueBackupTaskTest  {
     public void tearDown() throws Exception {
         ShadowBackupDataInput.reset();
         ShadowApplicationPackageManager.reset();
+        // False by default.
+        FeatureFlagUtils.setEnabled(
+                mContext, FeatureFlagUtils.BACKUP_NO_KV_DATA_CHANGE_CALLS, false);
     }
 
     @Test
@@ -2344,6 +2348,9 @@ public class KeyValueBackupTaskTest  {
     @Test
     public void testRunTask_whenNoDataToBackupOnFirstBackup_doesNotTellTransportOfBackup()
             throws Exception {
+        FeatureFlagUtils.setEnabled(
+                mContext, FeatureFlagUtils.BACKUP_NO_KV_DATA_CHANGE_CALLS, true);
+
         TransportMock transportMock = setUpInitializedTransport(mTransport);
         mBackupManagerService.setCurrentToken(0L);
         when(transportMock.transport.getCurrentRestoreSet()).thenReturn(1234L);
@@ -2361,6 +2368,9 @@ public class KeyValueBackupTaskTest  {
     @Test
     public void testRunTask_whenBackupHasCompletedAndThenNoDataChanges_transportGetsNotified()
             throws Exception {
+        FeatureFlagUtils.setEnabled(
+                mContext, FeatureFlagUtils.BACKUP_NO_KV_DATA_CHANGE_CALLS, true);
+
         TransportMock transportMock = setUpInitializedTransport(mTransport);
         when(transportMock.transport.getCurrentRestoreSet()).thenReturn(1234L);
         when(transportMock.transport.isAppEligibleForBackup(