Move system groups into their own backend

Delete 'Anonymous Users', 'Registered Users', 'Project Owners' and
'Change Owner' from the database and account_groups table.  Define
them inside of a specialized SystemGroupBackend class.

Change-Id: Ia67add4630579f3d0ce25edcfd662bbcf918dc8f

gerrit-server/src/main/java/com/google/gerrit/server/schema/Schema_87.java

@@ -0,0 +1,68 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.schema;
+
+import com.google.gerrit.reviewdb.client.AccountGroup;
+import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.group.SystemGroupBackend;
+import com.google.gwtorm.jdbc.JdbcSchema;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+public class Schema_87 extends SchemaVersion {
+  @Inject
+  Schema_87(Provider<Schema_86> prior) {
+    super(prior);
+  }
+
+  @Override
+  protected void migrateData(ReviewDb db, UpdateUI ui)
+      throws OrmException, SQLException {
+    for (AccountGroup.Id id : scanSystemGroups(db)) {
+      AccountGroup group = db.accountGroups().get(id);
+      if (group != null
+          && SystemGroupBackend.isSystemGroup(group.getGroupUUID())) {
+        db.accountGroups().delete(Collections.singleton(group));
+        db.accountGroupNames().deleteKeys(
+            Collections.singleton(group.getNameKey()));
+      }
+    }
+  }
+
+  private Set<AccountGroup.Id> scanSystemGroups(ReviewDb db)
+      throws SQLException {
+    JdbcSchema s = (JdbcSchema) db;
+    Statement stmt = s.getConnection().createStatement();
+    try {
+      ResultSet rs =
+          stmt.executeQuery("SELECT group_id FROM account_groups WHERE group_type = 'SYSTEM'");
+      Set<AccountGroup.Id> ids = new HashSet<>();
+      while (rs.next()) {
+        ids.add(new AccountGroup.Id(rs.getInt(1)));
+      }
+      return ids;
+    } finally {
+      stmt.close();
+    }
+  }
+}