[presubmit] Enable readability/namespace linter checking.

src/x64/codegen-x64.h

 // Copyright 2011 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_X64_CODEGEN_X64_H_
 #define V8_X64_CODEGEN_X64_H_
 
 #include "src/ast.h"
 #include "src/macro-assembler.h"
 
@@ skipping 90 matching lines @@
   const Register base_reg_;
   const Register argument_count_reg_;
   const int argument_count_immediate_;
   const StackArgumentsAccessorReceiverMode receiver_mode_;
   const int extra_displacement_to_last_argument_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(StackArgumentsAccessor);
 };
 
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_X64_CODEGEN_X64_H_