[presubmit] Enable readability/namespace linter checking.

src/diy-fp.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_DIY_FP_H_
 #define V8_DIY_FP_H_
 
 #include <stdint.h>
 
 #include "src/base/logging.h"
@@ skipping 75 matching lines @@
   void set_f(uint64_t new_value) { f_ = new_value; }
   void set_e(int new_value) { e_ = new_value; }
 
  private:
   static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
 
   uint64_t f_;
   int e_;
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_DIY_FP_H_