EDK: Sprinkle some more |final| secret sauce.

mojo/edk/system/test/stopwatch.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // A simple "stopwatch" for measuring elapsed time.
 
 #ifndef MOJO_EDK_SYSTEM_TEST_STOPWATCH_H_
 #define MOJO_EDK_SYSTEM_TEST_STOPWATCH_H_
 
 #include "mojo/edk/embedder/simple_platform_support.h"
 #include "mojo/public/c/system/types.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
 namespace system {
 namespace test {
 
 // A simple "stopwatch" for measuring time elapsed from a given starting point.
-class Stopwatch {
+class Stopwatch final {
  public:
   Stopwatch();
   ~Stopwatch();
 
   void Start();
   // Returns the amount of time elapsed since the last call to |Start()| (in
   // microseconds).
   MojoDeadline Elapsed();
 
  private:
   // TODO(vtl): We need this for |GetTimeTicksNow()|. Maybe we should have a
   // singleton for tests instead? Or maybe it should be injected?
   embedder::SimplePlatformSupport platform_support_;
 
   MojoTimeTicks start_time_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(Stopwatch);
 };
 
 }  // namespace test
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_TEST_STOPWATCH_H_