Export LifecycleListener in the extension API

Extensions may need to know when they are starting or stopping.
Export the interface that they can use to learn this information.

Change-Id: I45bb567aa76887844fbd82c8394ef117aa69c77c

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/events/LifecycleListener.java

@@ -0,0 +1,29 @@
+// Copyright (C) 2009 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.extensions.events;
+
+import com.google.gerrit.extensions.annotations.ExtensionPoint;
+
+import java.util.EventListener;
+
+/** Listener interested in server startup and shutdown events. */
+@ExtensionPoint
+public interface LifecycleListener extends EventListener {
+  /** Invoke when the server is starting. */
+  public void start();
+
+  /** Invoked when the server is stopping. */
+  public void stop();
+}