Add RefPermission#fromName and test it

Change-Id: I707cddcb96f970cbc534ace4d3e92bb6de324333

java/com/google/gerrit/server/permissions/RefPermission.java

@@ -15,6 +15,7 @@
 package com.google.gerrit.server.permissions;
 
 import com.google.gerrit.common.data.Permission;
+import java.util.Arrays;
 import java.util.Locale;
 import java.util.Optional;
 
@@ -80,4 +81,9 @@ public enum RefPermission {
   public String describeForException() {
     return toString().toLowerCase(Locale.US).replace('_', ' ');
   }
+
+  /** @return the enum constant for a given permission name if present. */
+  public static Optional<RefPermission> fromName(String name) {
+    return Arrays.stream(RefPermission.values()).filter(p -> name.equals(p.name)).findFirst();
+  }
 }

javatests/com/google/gerrit/server/permissions/RefPermissionTest.java

@@ -0,0 +1,30 @@
+// Copyright (C) 2018 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.permissions;
+
+import static com.google.common.truth.Truth8.assertThat;
+
+import com.google.gerrit.common.data.Permission;
+import org.junit.Test;
+
+public class RefPermissionTest {
+  @Test
+  public void fromName() {
+    assertThat(RefPermission.fromName("doesnotexist")).isEmpty();
+    assertThat(RefPermission.fromName("")).isEmpty();
+    assertThat(RefPermission.fromName(Permission.VIEW_PRIVATE_CHANGES))
+        .hasValue(RefPermission.READ_PRIVATE_CHANGES);
+  }
+}