[presubmit] Enable readability/namespace linter checking.

src/v8threads.h

 // 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.
 
 #ifndef V8_V8THREADS_H_
 #define V8_V8THREADS_H_
 
 #include "src/isolate.h"
 
 namespace v8 {
@@ skipping 100 matching lines @@
   // Head of linked list of states in use.
   ThreadState* in_use_anchor_;
 
   Isolate* isolate_;
 
   friend class Isolate;
   friend class ThreadState;
 };
 
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_V8THREADS_H_