[presubmit] Enable readability/namespace linter checking.

src/mips64/constants-mips64.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_MIPS_CONSTANTS_H_
 #define  V8_MIPS_CONSTANTS_H_
 
 #include "src/base/logging.h"
 #include "src/base/macros.h"
 #include "src/globals.h"
@@ skipping 1224 matching lines @@
         return kImmediateType;
       } else {
         return kUnsupported;
       }
   }
   return kUnsupported;
 }
 
 #undef OpcodeToBitNumber
 #undef FunctionFieldToBitNumber
-} }   // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif    // #ifndef V8_MIPS_CONSTANTS_H_