[presubmit] Enable readability/namespace linter checking.

src/bignum.h

 // Copyright 2010 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_BIGNUM_H_
 #define V8_BIGNUM_H_
 
 #include "src/vector.h"
 
 namespace v8 {
@@ skipping 97 matching lines @@
   // A vector backed by bigits_buffer_. This way accesses to the array are
   // checked for out-of-bounds errors.
   Vector<Chunk> bigits_;
   int used_digits_;
   // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
   int exponent_;
 
   DISALLOW_COPY_AND_ASSIGN(Bignum);
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_BIGNUM_H_