Move all FooterKeys into one place

We want to have the common FooterKeys be setup in one place, preventing
typo mistakes when reusing them.

Change-Id: Id31652bf0f0415c7b1a72df4f034910245a1d690

gerrit-server/src/main/java/com/google/gerrit/common/FooterConstants.java

@@ -0,0 +1,31 @@
+// 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.common;
+
+import org.eclipse.jgit.revwalk.FooterKey;
+
+public class FooterConstants {
+  /** The change ID as used to track patch sets. */
+  public static final FooterKey CHANGE_ID = new FooterKey("Change-Id");
+
+  /** The footer telling us who reviewed the change. */
+  public static final FooterKey REVIEWED_BY = new FooterKey("Reviewed-by");
+
+  /** The footer telling us the URL where the review took place. */
+  public static final FooterKey REVIEWED_ON = new FooterKey("Reviewed-on");
+
+  /** The footer telling us who tested the change. */
+  public static final FooterKey TESTED_BY = new FooterKey("Tested-by");
+}