Move flags extension exceptions to separate classes

The exceptions created for generic problems with the flags extension (invalid flag, etc.) should be in a common location, so they can be used by all interested TLDs.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=133040831

java/google/registry/flows/domain/flags/ExtensionFlagSetDomainPolicyErrorException.java

@@ -0,0 +1,24 @@
+// Copyright 2016 The Domain Registry 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.domain.flags;
+
+import google.registry.flows.EppException.StatusProhibitsOperationException;
+
+/** Extension flag cannot currently be set for this domain. */
+public class ExtensionFlagSetDomainPolicyErrorException extends StatusProhibitsOperationException {
+  public ExtensionFlagSetDomainPolicyErrorException(String flag) {
+    super(String.format("Extension flag %s cannot be set for this domain", flag));
+  }
+}