Add serializer for Permission

This commit adds a serializer for the Permission entitiy. The
eventual goal is that we serialize CachedProjectConfig. The entity
is too large to be serialized directly, though, so we divide and
conquer.

Change-Id: Ia1bfe912f15ddb3d5c2e2bab4586944550845eb5

javatests/com/google/gerrit/server/cache/serialize/entities/PermissionSerializerTest.java

@@ -0,0 +1,42 @@
+// Copyright (C) 2020 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.cache.serialize.entities;
+
+import static com.google.common.truth.Truth.assertThat;
+import static com.google.gerrit.server.cache.serialize.entities.PermissionSerializer.deserialize;
+import static com.google.gerrit.server.cache.serialize.entities.PermissionSerializer.serialize;
+
+import com.google.gerrit.common.data.GroupReference;
+import com.google.gerrit.common.data.Permission;
+import com.google.gerrit.common.data.PermissionRule;
+import org.junit.Test;
+
+public class PermissionSerializerTest {
+  @Test
+  public void roundTrip() {
+    Permission permissionRuleAutoValue =
+        Permission.builder(Permission.ABANDON)
+            .setExclusiveGroup(true)
+            .add(PermissionRule.builder(GroupReference.create("group")))
+            .build();
+    assertThat(deserialize(serialize(permissionRuleAutoValue))).isEqualTo(permissionRuleAutoValue);
+  }
+
+  @Test
+  public void roundTripWithMinimalValues() {
+    Permission permission = Permission.builder(Permission.ABANDON).build();
+    assertThat(deserialize(serialize(permission))).isEqualTo(permission);
+  }
+}