[presubmit] Enable readability/namespace linter checking.

src/regexp/x64/regexp-macro-assembler-x64.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_REGEXP_X64_REGEXP_MACRO_ASSEMBLER_X64_H_
 #define V8_REGEXP_X64_REGEXP_MACRO_ASSEMBLER_X64_H_
 
 #include "src/macro-assembler.h"
 #include "src/regexp/regexp-macro-assembler.h"
 #include "src/x64/assembler-x64.h"
@@ skipping 258 matching lines @@
   Label start_label_;
   Label success_label_;
   Label backtrack_label_;
   Label exit_label_;
   Label check_preempt_label_;
   Label stack_overflow_label_;
 };
 
 #endif  // V8_INTERPRETED_REGEXP
 
-}}  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_REGEXP_X64_REGEXP_MACRO_ASSEMBLER_X64_H_