base: Add/Fix namespace closing comments.

base/test/null_task_runner.h

 // Copyright (c) 2012 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.
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/single_thread_task_runner.h"
 
 namespace base {
 
@@ skipping 12 matching lines @@
                                   base::TimeDelta delay) override;
   // Always returns true to avoid triggering DCHECKs.
   bool RunsTasksOnCurrentThread() const override;
 
  protected:
   ~NullTaskRunner() override;
 
   DISALLOW_COPY_AND_ASSIGN(NullTaskRunner);
 };
 
-}  // namespace
+}  // namespace base