Move GCP proxy code to the old [] proxy's location

1. Moved code for the GCP proxy to where the [] proxy code used to live.
3. Corrected reference to the GCP proxy location.
4. Misc changes to make ErrorProne and various tools happy.

+diekmann to LGTM terraform whitelist change.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=213630560

javatests/google/registry/proxy/handler/HealthCheckHandlerTest.java

@@ -0,0 +1,58 @@
+// Copyright 2017 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.proxy.handler;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.nio.charset.StandardCharsets.US_ASCII;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
+import io.netty.channel.embedded.EmbeddedChannel;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link HealthCheckHandler}. */
+@RunWith(JUnit4.class)
+public class HealthCheckHandlerTest {
+
+  private static final String CHECK_REQ = "REQUEST";
+  private static final String CHECK_RES = "RESPONSE";
+
+  private final HealthCheckHandler healthCheckHandler =
+      new HealthCheckHandler(CHECK_REQ, CHECK_RES);
+  private final EmbeddedChannel channel = new EmbeddedChannel(healthCheckHandler);
+
+  @Test
+  public void testSuccess_ResponseSent() {
+    ByteBuf input = Unpooled.wrappedBuffer(CHECK_REQ.getBytes(US_ASCII));
+    // No inbound message passed to the next handler.
+    assertThat(channel.writeInbound(input)).isFalse();
+    ByteBuf output = channel.readOutbound();
+    assertThat(channel.isActive()).isTrue();
+    assertThat(output.toString(US_ASCII)).isEqualTo(CHECK_RES);
+  }
+
+  @Test
+  public void testSuccess_IgnoreUnrecognizedRequest() {
+    String unrecognizedInput = "1234567";
+    ByteBuf input = Unpooled.wrappedBuffer(unrecognizedInput.getBytes(US_ASCII));
+    // No inbound message passed to the next handler.
+    assertThat(channel.writeInbound(input)).isFalse();
+    // No response is sent.
+    assertThat(channel.isActive()).isTrue();
+    assertThat((Object) channel.readOutbound()).isNull();
+  }
+}