Tighten up the "define" classes.

Change-Id: I854b1dd56b676d0a492a15c16bfe4c6a1bcccdf7

java/src/com/android/inputmethod/latin/define/JniLibName.java

@@ -16,6 +16,10 @@
 
 package com.android.inputmethod.latin.define;
 
-public class JniLibName {
+public final class JniLibName {
+    private JniLibName() {
+        // This class is not publicly instantiable.
+    }
+
     public static final String JNI_LIB_NAME = "jni_latinime";
 }

java/src/com/android/inputmethod/latin/define/ProductionFlag.java

@@ -16,6 +16,10 @@
 
 package com.android.inputmethod.latin.define;
 
-public class ProductionFlag {
+public final class ProductionFlag {
+    private ProductionFlag() {
+        // This class is not publicly instantiable.
+    }
+
     public static final boolean IS_EXPERIMENTAL = false;
 }