RefInfo: Add implementation of toString

Change-Id: I3833c23725fda688a32be2818696db47fc58565a
diff --git a/java/com/google/gerrit/extensions/api/projects/RefInfo.java b/java/com/google/gerrit/extensions/api/projects/RefInfo.java
index c573600..d5695fd 100644
--- a/java/com/google/gerrit/extensions/api/projects/RefInfo.java
+++ b/java/com/google/gerrit/extensions/api/projects/RefInfo.java
@@ -14,8 +14,15 @@
 
 package com.google.gerrit.extensions.api.projects;
 
+import com.google.common.base.MoreObjects;
+
 public class RefInfo {
   public String ref;
   public String revision;
   public Boolean canDelete;
+
+  @Override
+  public String toString() {
+    return MoreObjects.toStringHelper(this).add("ref", ref).add("revision", revision).toString();
+  }
 }