Events: Add GerritEvent and ProjectEvent interfaces

In the current implementation the event interfaces don't share a common
base interface, which means it's not possible for users to refer to them
in a generic way.

Add a GerritEvent interface from which all events now inherit. This makes
it possible to define, for example, a list:

  List<GerritEvent> events

and add any of the derived event types.

Also add a new intermediate interface, ProjectEvent, and modify all the
existing project-related events to derive from it.

Change-Id: I62ccd8f0b172e1d1e432d84ca3e20d088480be20

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

@@ -20,7 +20,7 @@ import com.google.gerrit.extensions.common.AccountInfo;
 /** Notified whenever a user signed up for a Contributor License Agreement. */
 @ExtensionPoint
 public interface AgreementSignupListener {
-  interface Event {
+  interface Event extends GerritEvent {
     AccountInfo getAccount();
     String getAgreementName();
   }

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

@@ -17,7 +17,7 @@ package com.google.gerrit.extensions.events;
 import com.google.gerrit.extensions.common.ChangeInfo;
 
 /** Interface to be extended by Events with a Change. */
-public interface ChangeEvent {
+public interface ChangeEvent extends GerritEvent {
   ChangeInfo getChange();
 }
 

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

@@ -23,10 +23,7 @@ import java.util.Properties;
  */
 @ExtensionPoint
 public interface GarbageCollectorListener {
-  interface Event {
-    /** @return The name of the project that has been garbage collected. */
-    String getProjectName();
-
+  interface Event extends ProjectEvent {
     /**
      * @return Properties describing the result of the garbage collection
      *         performed by JGit.

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

@@ -0,0 +1,19 @@
+// Copyright (C) 2016 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;
+
+/** Base interface to be extended by Events. */
+public interface GerritEvent {
+}

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

@@ -21,9 +21,7 @@ import com.google.gerrit.extensions.common.AccountInfo;
 /** Notified when one or more references are modified. */
 @ExtensionPoint
 public interface GitReferenceUpdatedListener {
-
-  interface Event {
-    String getProjectName();
+  interface Event extends ProjectEvent {
     String getRefName();
     String getOldObjectId();
     String getNewObjectId();

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

@@ -19,8 +19,7 @@ import com.google.gerrit.extensions.annotations.ExtensionPoint;
 /** Notified whenever the HEAD of a project is updated. */
 @ExtensionPoint
 public interface HeadUpdatedListener {
-  interface Event {
-    String getProjectName();
+  interface Event extends ProjectEvent {
     String getOldHeadName();
     String getNewHeadName();
   }

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

@@ -20,8 +20,7 @@ import com.google.gerrit.extensions.annotations.ExtensionPoint;
 /** Notified whenever a project is created on the master. */
 @ExtensionPoint
 public interface NewProjectCreatedListener {
-  interface Event {
-    String getProjectName();
+  interface Event extends ProjectEvent {
     String getHeadName();
   }
 

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

@@ -16,7 +16,7 @@ package com.google.gerrit.extensions.events;
 
 /** Notified when a plugin fires an event. */
 public interface PluginEventListener {
-  interface Event {
+  interface Event extends GerritEvent {
     String pluginName();
     String getType();
     String getData();

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

@@ -19,8 +19,7 @@ import com.google.gerrit.extensions.annotations.ExtensionPoint;
 /** Notified whenever a project is deleted on the master. */
 @ExtensionPoint
 public interface ProjectDeletedListener {
-  interface Event {
-    String getProjectName();
+  interface Event extends ProjectEvent {
   }
 
   void onProjectDeleted(Event event);

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

@@ -0,0 +1,20 @@
+// Copyright (C) 2016 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;
+
+/** Interface to be extended by Events with a Project. */
+public interface ProjectEvent extends GerritEvent {
+  String getProjectName();
+}