Clean up some code quality issues in GCP proxy

All changes are suggested by IntelliJ code inspection.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=189586104

javatests/google/registry/proxy/GcpJsonFormatterTest.java

@@ -37,16 +37,13 @@ public class GcpJsonFormatterTest {
   private final LogRecord logRecord = new LogRecord(Level.WARNING, MESSAGE);
 
   private static String makeJson(String severity, String source, String message) {
-    StringBuilder builder = new StringBuilder();
-    builder.append("{");
-    builder.append(
-        Joiner.on(",")
+    return "{"
+        + Joiner.on(",")
             .join(
                 makeJsonField("severity", severity),
                 makeJsonField("source", source),
-                makeJsonField("message", "\\n" + message)));
-    builder.append("}\n");
-    return builder.toString();
+                makeJsonField("message", "\\n" + message))
+        + "}\n";
   }
 
   private static String makeJsonField(String name, String content) {

javatests/google/registry/proxy/ProtocolModuleTest.java

@@ -18,7 +18,6 @@ import static com.google.common.collect.ImmutableList.toImmutableList;
 import static google.registry.proxy.ProxyConfig.Environment.TEST;
 import static google.registry.proxy.ProxyConfig.getProxyConfig;
 
-import com.google.common.base.Supplier;
 import com.google.common.base.Suppliers;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -55,6 +54,7 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 import javax.inject.Named;
 import javax.inject.Provider;
 import javax.inject.Singleton;

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

@@ -51,7 +51,7 @@ public class ProxyProtocolHandlerTest {
 
   @Test
   public void testSuccess_proxyHeaderMalformed_singleFrame() {
-    header = String.format("PROXY UNKNOWN\r\n");
+    header = "PROXY UNKNOWN\r\n";
     String message = "some message";
     // Header processed, rest of the message passed along.
     assertThat(channel.writeInbound(Unpooled.wrappedBuffer((header + message).getBytes(UTF_8))))

javatests/google/registry/proxy/metric/MetricParametersTest.java

@@ -62,8 +62,7 @@ public class MetricParametersTest {
           ZONE_PATH,
           zoneConnection);
   private final HashMap<String, String> fakeEnvVarMap = new HashMap<>();
-  private final Function<String, HttpURLConnection> fakeConnectionFactory =
-      path -> mockConnections.get(path);
+  private final Function<String, HttpURLConnection> fakeConnectionFactory = mockConnections::get;
 
   private final MetricParameters metricParameters =
       new MetricParameters(fakeEnvVarMap, fakeConnectionFactory);

javatests/google/registry/proxy/quota/QuotaManagerTest.java

@@ -46,7 +46,6 @@ public class QuotaManagerTest {
       new QuotaManager(tokenStore, MoreExecutors.newDirectExecutorService());
   private QuotaRequest request;
   private QuotaResponse response;
-  private QuotaRebate rebate;
 
   @Test
   public void testSuccess_requestApproved() {
@@ -74,7 +73,7 @@ public class QuotaManagerTest {
   public void testSuccess_rebate() throws Exception {
     DateTime grantedTokenRefillTime = clock.nowUtc();
     response = QuotaResponse.create(true, USER_ID, grantedTokenRefillTime);
-    rebate = QuotaRebate.create(response);
+    QuotaRebate rebate = QuotaRebate.create(response);
     Future<?> unusedFuture = quotaManager.releaseQuota(rebate);
     verify(tokenStore).scheduleRefresh();
     verify(tokenStore).put(USER_ID, grantedTokenRefillTime);