Fix deprecated EMPTY_ARRAY usage (nanoprotos).

Newer nanoproto compiler discourages the use of this.

Change-Id: Ic27a6d15f2892bb49df3100147c086a2bce20fd4

src/com/android/launcher3/LauncherBackupHelper.java

@@ -193,7 +193,7 @@ public class LauncherBackupHelper implements BackupHelper {
             Log.e(TAG, "launcher backup has failed", e);
         }
 
-        out.key = keys.toArray(BackupProtos.Key.EMPTY_ARRAY);
+        out.key = keys.toArray(new BackupProtos.Key[keys.size()]);
         writeJournal(newState, out);
         Log.v(TAG, "onBackup: wrote " + out.bytes + "b in " + out.rows + " rows.");
     }
@@ -266,7 +266,7 @@ public class LauncherBackupHelper implements BackupHelper {
         // will catch any changes the restore process might have made
         Journal out = new Journal();
         out.t = 0;
-        out.key = mKeys.toArray(BackupProtos.Key.EMPTY_ARRAY);
+        out.key = mKeys.toArray(new BackupProtos.Key[mKeys.size()]);
         writeJournal(newState, out);
         Log.v(TAG, "onRestore: read " + mKeys.size() + " rows");
         mKeys.clear();