Refactor common email sending utility

The main thrust of this is to create a common POJO that contains email content in a simple way, then have one class that converts that to an email and sends it. Any class that uses email should only have to deal with creating that POJO.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=237883643

java/google/registry/util/TransportEmailSender.java

@@ -0,0 +1,34 @@
+// Copyright 2019 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.util;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+import javax.mail.Message;
+import javax.mail.MessagingException;
+import javax.mail.Transport;
+
+/** Wrapper for sending email so that we can test {@link google.registry.util.SendEmailService}. */
+@Singleton
+class TransportEmailSender {
+
+  @Inject
+  TransportEmailSender() {}
+
+  /** Sends a message using default App Engine transport. */
+  void sendMessage(Message msg) throws MessagingException {
+    Transport.send(msg);
+  }
+}