Add extra flow logic hook for application create

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=137396935

javatests/google/registry/flows/domain/DomainApplicationCreateFlowTest.java

@@ -105,6 +105,8 @@ import google.registry.flows.exceptions.ResourceAlreadyExistsException;
 import google.registry.model.domain.DomainApplication;
 import google.registry.model.domain.GracePeriod;
 import google.registry.model.domain.LrpTokenEntity;
+import google.registry.model.domain.TestExtraLogicManager;
+import google.registry.model.domain.TestExtraLogicManager.TestExtraLogicManagerSuccessException;
 import google.registry.model.domain.launch.ApplicationStatus;
 import google.registry.model.domain.launch.LaunchNotice;
 import google.registry.model.domain.launch.LaunchPhase;
@@ -155,6 +157,10 @@ public class DomainApplicationCreateFlowTest
     setEppInput("domain_create_sunrise_encoded_signed_mark.xml");
     createTld("tld", TldState.SUNRISE);
     persistResource(Registry.get("tld").asBuilder().setReservedLists(createReservedList()).build());
+    createTld("flags", TldState.LANDRUSH);
+    RegistryExtraFlowLogicProxy.setOverride("flags", TestExtraLogicManager.class);
+    persistResource(
+        Registry.get("flags").asBuilder().setReservedLists(createReservedList()).build());
     inject.setStaticField(TmchCertificateAuthority.class, "clock", clock);
     clock.setTo(DateTime.parse("2014-09-09T09:09:09Z"));
   }
@@ -1686,4 +1692,20 @@ public class DomainApplicationCreateFlowTest
     // ❤☀☆☂☻♞☯.tld
     doFailingDomainNameTest("xn--k3hel9n7bxlu1e.tld", InvalidIdnDomainLabelException.class);
   }
+
+  @Test
+  public void testFailure_flags_feeMismatch() throws Exception {
+    persistContactsAndHosts();
+    setEppInput("domain_create_landrush_flags.xml", ImmutableMap.of("FEE", "12"));
+    thrown.expect(FeesMismatchException.class);
+    runFlow();
+  }
+
+  @Test
+  public void testSuccess_flags() throws Exception {
+    persistContactsAndHosts();
+    setEppInput("domain_create_landrush_flags.xml", ImmutableMap.of("FEE", "42"));
+    thrown.expect(TestExtraLogicManagerSuccessException.class, "flag1,flag2");
+    runFlow();
+  }
 }

javatests/google/registry/flows/domain/testdata/domain_create_landrush_flags.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
+  <command>
+    <create>
+      <domain:create
+       xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
+        <domain:name>create-42.flags</domain:name>
+        <domain:ns>
+          <domain:hostObj>ns1.example.net</domain:hostObj>
+          <domain:hostObj>ns2.example.net</domain:hostObj>
+        </domain:ns>
+        <domain:registrant>jd1234</domain:registrant>
+        <domain:contact type="admin">sh8013</domain:contact>
+        <domain:contact type="tech">sh8013</domain:contact>
+        <domain:authInfo>
+          <domain:pw>2fooBAR</domain:pw>
+        </domain:authInfo>
+      </domain:create>
+    </create>
+    <extension>
+      <launch:create
+       xmlns:launch="urn:ietf:params:xml:ns:launch-1.0">
+        <launch:phase>landrush</launch:phase>
+      </launch:create>
+      <fee:create xmlns:fee="urn:ietf:params:xml:ns:fee-0.6">
+        <fee:currency>USD</fee:currency>
+        <fee:fee>%FEE%</fee:fee>
+      </fee:create>
+      <flags:create xmlns:flags="urn:google:params:xml:ns:flags-0.1">
+        <flags:flag>flag1</flags:flag>
+        <flags:flag>flag2</flags:flag>
+      </flags:create>
+    </extension>
+    <clTRID>ABC-12345</clTRID>
+  </command>
+</epp>

javatests/google/registry/model/domain/TestExtraLogicManager.java

@@ -99,6 +99,26 @@ public class TestExtraLogicManager implements RegistryExtraFlowLogic {
     }
   }
 
+  /**
+   * Performs additional tasks required for an application create command. Any changes should not be
+   * persisted to Datastore until commitAdditionalLogicChanges is called.
+   */
+  @Override
+  public void performAdditionalApplicationCreateLogic(
+      DomainApplication application,
+      String clientId,
+      DateTime asOfDate,
+      int years,
+      EppInput eppInput,
+      HistoryEntry historyEntry) throws EppException {
+    FlagsCreateCommandExtension flags =
+        eppInput.getSingleExtension(FlagsCreateCommandExtension.class);
+    if (flags == null) {
+      return;
+    }
+    messageToThrow = Joiner.on(',').join(flags.getFlags());
+  }
+
   /** Computes the expected create cost, for use in fee challenges and the like. */
   @Override
   public BaseFee getCreateFeeOrCredit(