EDK: Sprinkle some more |final| secret sauce.

mojo/edk/system/test/scoped_test_dir.h

Index: mojo/edk/system/test/scoped_test_dir.h
diff --git a/mojo/edk/system/test/scoped_test_dir.h b/mojo/edk/system/test/scoped_test_dir.h
index 9f4db1bb3d2d2d0e8e3cb6004d2721f3ec510ce4..9d4fde8fbbdd114eaa984a29c46eb9c1a0a8d34f 100644
--- a/mojo/edk/system/test/scoped_test_dir.h
+++ b/mojo/edk/system/test/scoped_test_dir.h
@@ -15,7 +15,7 @@ namespace test {
 
 // Creates/destroyes a temporary directory for test purposes. (Unlike
 // |base::ScopedTempDir|, this automatically creates the temporary directory.)
-class ScopedTestDir {
+class ScopedTestDir final {
  public:
   ScopedTestDir();
   ~ScopedTestDir();