[presubmit] Enable readability/namespace linter checking.

src/codegen.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_CODEGEN_H_
 #define V8_CODEGEN_H_
 
 #include "src/code-stubs.h"
 #include "src/runtime/runtime.h"
 
@@ skipping 152 matching lines @@
 
  protected:
   const EmbeddedVector<byte, kNoCodeAgeSequenceLength> young_sequence_;
 #ifdef DEBUG
 #ifdef V8_TARGET_ARCH_ARM64
   const EmbeddedVector<byte, kNoCodeAgeSequenceLength> old_sequence_;
 #endif
 #endif
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_CODEGEN_H_