Introduce ref operation validation

Create extension point that is responsible for ref operations validation.

Change-Id: Ia6386ce6480ae63b75ec3b2836267c2f8d68d426
Signed-off-by: Jacek Centkowski <geminica.programs@gmail.com>

gerrit-server/src/main/java/com/google/gerrit/server/events/RefOperationReceivedEvent.java

@@ -0,0 +1,26 @@
+// Copyright (C) 2014 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.events;
+
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.server.IdentifiedUser;
+
+import org.eclipse.jgit.transport.ReceiveCommand;
+
+public class RefOperationReceivedEvent extends ChangeEvent {
+  public final String type = "ref-received";
+  public ReceiveCommand command;
+  public Project project;
+  public IdentifiedUser user;
+}