[presubmit] Enable readability/namespace linter checking.

src/vector.h

 // Copyright 2014 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_VECTOR_H_
 #define V8_VECTOR_H_
 
 #include <string.h>
 #include <algorithm>
 
@@ skipping 184 matching lines @@
 inline Vector<char> MutableCStrVector(char* data) {
   return Vector<char>(data, StrLength(data));
 }
 
 inline Vector<char> MutableCStrVector(char* data, int max) {
   int length = StrLength(data);
   return Vector<char>(data, (length < max) ? length : max);
 }
 
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_VECTOR_H_