DeReference the codebase

This change replaces all Ref objects in the code with Key objects. These are
stored in datastore as the same object (raw datastore keys), so this is not
a model change.

Our best practices doc says to use Keys not Refs because:
 * The .get() method obscures what's actually going on
   - Much harder to visually audit the code for datastore loads
   - Hard to distinguish Ref<T> get()'s from Optional get()'s and Supplier get()'s
 * Implicit ofy().load() offers much less control
   - Antipattern for ultimate goal of making Ofy injectable
   - Can't control cache use or batch loading without making ofy() explicit anyway
 * Serialization behavior is surprising and could be quite dangerous/incorrect
   - Can lead to serialization errors. If it actually worked "as intended",
     it would lead to a Ref<> on a serialized object being replaced upon
     deserialization with a stale copy of the old value, which could potentially
     break all kinds of transactional expectations
 * Having both Ref<T> and Key<T> introduces extra boilerplate everywhere
   - E.g. helper methods all need to have Ref and Key overloads, or you need to
     call .key() to get the Key<T> for every Ref<T> you want to pass in
   - Creating a Ref<T> is more cumbersome, since it doesn't have all the create()
     overloads that Key<T> has, only create(Key<T>) and create(Entity) - no way to
     create directly from kind+ID/name, raw Key, websafe key string, etc.

(Note that Refs are treated specially by Objectify's @Load method and Keys are not;
we don't use that feature, but it is the one advantage Refs have over Keys.)

The direct impetus for this change is that I am trying to audit our use of memcache,
and the implicit .get() calls to datastore were making that very hard.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=131965491

java/google/registry/model/host/HostResource.java

@@ -17,13 +17,14 @@ package google.registry.model.host;
 import static com.google.common.collect.Sets.difference;
 import static com.google.common.collect.Sets.union;
 import static google.registry.model.EppResourceUtils.projectResourceOntoBuilderAtTime;
+import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.model.ofy.Ofy.RECOMMENDED_MEMCACHE_EXPIRATION;
 import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
 import static google.registry.util.DateTimeUtils.START_OF_TIME;
 
 import com.google.common.base.Optional;
 import com.google.common.collect.ImmutableSet;
-import com.googlecode.objectify.Ref;
+import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.Cache;
 import com.googlecode.objectify.annotation.Entity;
 import com.googlecode.objectify.annotation.IgnoreSave;
@@ -88,7 +89,7 @@ public class HostResource extends EppResource implements ForeignKeyedEppResource
   @Index
   @IgnoreSave(IfNull.class)
   @XmlTransient
-  Ref<DomainResource> superordinateDomain;
+  Key<DomainResource> superordinateDomain;
 
   /**
    * The most recent time that the superordinate domain was changed, or null if this host is
@@ -102,7 +103,7 @@ public class HostResource extends EppResource implements ForeignKeyedEppResource
     return fullyQualifiedHostName;
   }
 
-  public Ref<DomainResource> getSuperordinateDomain() {
+  public Key<DomainResource> getSuperordinateDomain() {
     return superordinateDomain;
   }
 
@@ -132,7 +133,8 @@ public class HostResource extends EppResource implements ForeignKeyedEppResource
     } else {
       // For hosts with superordinate domains, the client id, last transfer time, and transfer data
       // need to be read off the domain projected to the correct time.
-      DomainResource domainAtTime = superordinateDomain.get().cloneProjectedAtTime(now);
+      DomainResource domainAtTime = ofy().load().key(superordinateDomain).now()
+          .cloneProjectedAtTime(now);
       builder.setCurrentSponsorClientId(domainAtTime.getCurrentSponsorClientId());
       // If the superordinate domain's last transfer time is what is relevant, because the host's
       // superordinate domain was last changed less recently than the domain's last transfer, then
@@ -192,7 +194,7 @@ public class HostResource extends EppResource implements ForeignKeyedEppResource
           difference(getInstance().getInetAddresses(), inetAddresses)));
     }
 
-    public Builder setSuperordinateDomain(Ref<DomainResource> superordinateDomain) {
+    public Builder setSuperordinateDomain(Key<DomainResource> superordinateDomain) {
       getInstance().superordinateDomain = superordinateDomain;
       return this;
     }