[presubmit] Enable readability/namespace linter checking.

src/x64/lithium-codegen-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_X64_LITHIUM_CODEGEN_X64_H_
 #define V8_X64_LITHIUM_CODEGEN_X64_H_
 
 #include "src/x64/lithium-x64.h"
 
 #include "src/base/logging.h"
@@ skipping 369 matching lines @@
 
  private:
   LCodeGen* codegen_;
   Label entry_;
   Label exit_;
   Label done_;
   Label* external_exit_;
   int instruction_index_;
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_X64_LITHIUM_CODEGEN_X64_H_