[presubmit] Enable readability/namespace linter checking.

src/base/platform/semaphore.cc

 // Copyright 2013 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/platform/semaphore.h"
 
 #if V8_OS_MACOSX
 #include <mach/mach_init.h>
 #include <mach/task.h>
 #endif
@@ skipping 183 matching lines @@
         return false;
       }
       DCHECK(result == WAIT_OBJECT_0);
       return true;
     }
   }
 }
 
 #endif  // V8_OS_MACOSX
 
-} }  // namespace v8::base
+}  // namespace base
+}  // namespace v8