Add extensible custom logic to the domain update flow

This also adds beforeValidation hook to DomainCreateCustomFlow.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139828346

java/google/registry/flows/custom/DomainUpdateFlowCustomLogic.java

@@ -0,0 +1,120 @@
+// Copyright 2016 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.flows.custom;
+
+import com.google.auto.value.AutoValue;
+import google.registry.flows.EppException;
+import google.registry.flows.SessionMetadata;
+import google.registry.flows.domain.DomainUpdateFlow;
+import google.registry.model.ImmutableObject;
+import google.registry.model.domain.DomainResource;
+import google.registry.model.eppinput.EppInput;
+import google.registry.model.reporting.HistoryEntry;
+
+/**
+ * A no-op base class for {@link DomainUpdateFlow} custom logic.
+ *
+ * <p>Extend this class and override the hook(s) to perform custom logic.
+ */
+public class DomainUpdateFlowCustomLogic extends BaseFlowCustomLogic {
+
+  protected DomainUpdateFlowCustomLogic(EppInput eppInput, SessionMetadata sessionMetadata) {
+    super(eppInput, sessionMetadata);
+  }
+
+  /** A hook that runs before any validation. This is useful to e.g. add allowable extensions. */
+  @SuppressWarnings("unused")
+  public void beforeValidation() throws EppException {
+    // Do nothing.
+  }
+
+  /** A hook that runs at the end of the validation step to perform additional validation. */
+  @SuppressWarnings("unused")
+  public void afterValidation(AfterValidationParameters parameters) throws EppException {
+    // Do nothing.
+  }
+
+  /**
+   * A hook that runs before new entities are persisted, allowing them to be changed.
+   *
+   * <p>It returns the actual entity changes that should be persisted to Datastore. It is important
+   * to be careful when changing the flow behavior for existing entities, because the core logic
+   * across many different flows expects the existence of these entities and many of the fields on
+   * them.
+   */
+  @SuppressWarnings("unused")
+  public EntityChanges beforeSave(BeforeSaveParameters parameters) throws EppException {
+    return parameters.entityChanges();
+  }
+
+  /** A class to encapsulate parameters for a call to {@link #afterValidation}. */
+  @AutoValue
+  public abstract static class AfterValidationParameters extends ImmutableObject {
+
+    public abstract DomainResource existingDomain();
+
+    public static Builder newBuilder() {
+      return new AutoValue_DomainUpdateFlowCustomLogic_AfterValidationParameters.Builder();
+    }
+
+    /** Builder for {@link AfterValidationParameters}. */
+    @AutoValue.Builder
+    public abstract static class Builder {
+
+      public abstract Builder setExistingDomain(DomainResource existingDomain);
+
+      public abstract AfterValidationParameters build();
+    }
+  }
+
+  /**
+   * A class to encapsulate parameters for a call to {@link #beforeSave}.
+   *
+   * <p>Note that both newDomain and historyEntry are included in entityChanges. They are also
+   * passed separately for convenience, but they are the same instance, and changes to them will
+   * also affect what is persisted from entityChanges.
+   */
+  @AutoValue
+  public abstract static class BeforeSaveParameters extends ImmutableObject {
+
+    public abstract DomainResource existingDomain();
+
+    public abstract DomainResource newDomain();
+
+    public abstract HistoryEntry historyEntry();
+
+
+    public abstract EntityChanges entityChanges();
+
+    public static Builder newBuilder() {
+      return new AutoValue_DomainUpdateFlowCustomLogic_BeforeSaveParameters.Builder();
+    }
+
+    /** Builder for {@link BeforeSaveParameters}. */
+    @AutoValue.Builder
+    public abstract static class Builder {
+
+      public abstract Builder setExistingDomain(DomainResource existingDomain);
+
+      public abstract Builder setNewDomain(DomainResource newDomain);
+
+      public abstract Builder setHistoryEntry(HistoryEntry historyEntry);
+
+      public abstract Builder setEntityChanges(EntityChanges entityChanges);
+
+      public abstract BeforeSaveParameters build();
+    }
+  }
+}