base: Add/Fix namespace closing comments.

base/test/null_task_runner.cc

 // 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/test/null_task_runner.h"
 
 namespace base {
 
 NullTaskRunner::NullTaskRunner() {}
 
@@ skipping 10 matching lines @@
     const tracked_objects::Location& from_here,
     const base::Closure& task,
     base::TimeDelta delay) {
   return false;
 }
 
 bool NullTaskRunner::RunsTasksOnCurrentThread() const {
   return true;
 }
 
-}  // namespace
+}  // namespace base