Mojo: Fix warnings when generating code for empty struct in java.

mojo/android/javatests/src/org/chromium/mojo/bindings/BindingsTest.java

Index: mojo/android/javatests/src/org/chromium/mojo/bindings/BindingsTest.java
diff --git a/mojo/android/javatests/src/org/chromium/mojo/bindings/BindingsTest.java b/mojo/android/javatests/src/org/chromium/mojo/bindings/BindingsTest.java
index d26955b248b18f1b5343241221abd799946d996b..efb227c491eca2aaf4c26dd4122a0686dfb7ff9e 100644
--- a/mojo/android/javatests/src/org/chromium/mojo/bindings/BindingsTest.java
+++ b/mojo/android/javatests/src/org/chromium/mojo/bindings/BindingsTest.java
@@ -20,6 +20,7 @@ import org.chromium.mojo.bindings.test.mojom.sample.Enum;
 import org.chromium.mojo.bindings.test.mojom.sample.Foo;
 import org.chromium.mojo.bindings.test.mojom.sample.InterfaceConstants;
 import org.chromium.mojo.bindings.test.mojom.sample.SampleServiceConstants;
+import org.chromium.mojo.bindings.test.mojom.test_structs.EmptyStruct;
 import org.chromium.mojo.system.DataPipe.ConsumerHandle;
 import org.chromium.mojo.system.DataPipe.ProducerHandle;
 import org.chromium.mojo.system.MessagePipeHandle;
@@ -237,4 +238,15 @@ public class BindingsTest extends TestCase {
         assertFooEquals(typicalFoo, deserializedFoo);
     }
 
+    /**
+     * Testing serialization of the EmptyStruct class.
+     */
+    @SmallTest
+    public void testEmptyStructSerialization() {
+        // Checking serialization and deserialization of a EmptyStruct object.
+        Message serializedStruct = new EmptyStruct().serialize(null);
+        EmptyStruct emptyStruct = EmptyStruct.deserialize(serializedStruct);
+        assertNotNull(emptyStruct);
+    }
+
 }