ChangeIndexedListener: Move to extension API

Move to the extension API and change the interface so as not to use
internal data types.

The only known user of this interface (sync-index plugin) only needs
the change ID anyway.

Change-Id: Ia2d44aeae9fdaaa6d1d1667c28b3a7197ad5a622

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

@@ -0,0 +1,27 @@
+// Copyright (C) 2015 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;
+
+/** Notified whenever a change is indexed or deleted from the index. */
+@ExtensionPoint
+public interface ChangeIndexedListener {
+  /** Invoked when a change is indexed. */
+  void onChangeIndexed(int id);
+
+  /** Invoked when a change is deleted from the index. */
+  void onChangeDeleted(int id);
+}