[presubmit] Enable readability/namespace linter checking.

src/base/once.cc

 // Copyright 2012 the V8 project 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 "src/base/once.h"
 
 #ifdef _WIN32
 #include <windows.h>
 #else
 #include <sched.h>
@@ skipping 32 matching lines @@
 #ifdef _WIN32
       ::Sleep(0);
 #else
       sched_yield();
 #endif
       state = Acquire_Load(once);
     }
   }
 }
 
-} }  // namespace v8::base
+}  // namespace base
+}  // namespace v8