Add @VirtualEntity checking to Ofy's deleteWithoutBackup()

This was an oversight I noticed ages ago, so resurrecting some old local changes I had to correct it.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=146812322

javatests/google/registry/testing/TestObject.java

@@ -17,10 +17,12 @@ package google.registry.testing;
 import static google.registry.model.common.EntityGroupRoot.getCrossTldKey;
 
 import com.googlecode.objectify.Key;
+import com.googlecode.objectify.ObjectifyService;
 import com.googlecode.objectify.annotation.Entity;
 import com.googlecode.objectify.annotation.Id;
 import com.googlecode.objectify.annotation.Parent;
 import google.registry.model.ImmutableObject;
+import google.registry.model.annotations.VirtualEntity;
 import google.registry.model.common.EntityGroupRoot;
 
 /**
@@ -28,6 +30,10 @@ import google.registry.model.common.EntityGroupRoot;
  */
 @Entity
 public class TestObject extends ImmutableObject {
+  static {
+    ObjectifyService.register(TestObject.class);  // Register this kind on first reference.
+  }
+
   @Parent
   Key<EntityGroupRoot> parent;
 
@@ -59,4 +65,30 @@ public class TestObject extends ImmutableObject {
     instance.parent = parent;
     return instance;
   }
+
+  /** A test @VirtualEntity model object, which should not be persisted. */
+  @Entity
+  @VirtualEntity
+  public static class TestVirtualObject extends ImmutableObject {
+    static {
+      ObjectifyService.register(TestVirtualObject.class);  // Register this kind on first reference.
+    }
+
+    @Id
+    String id;
+
+    /**
+     * Expose a factory method for testing saves of virtual entities; in real life this would never
+     * be needed for an actual @VirtualEntity.
+     */
+    public static TestVirtualObject create(String id) {
+      TestVirtualObject instance = new TestVirtualObject();
+      instance.id = id;
+      return instance;
+    }
+
+    public static Key<TestVirtualObject> createKey(String id) {
+      return Key.create(TestVirtualObject.class, id);
+    }
+  }
 }