[presubmit] Enable readability/namespace linter checking.

src/ppc/constants-ppc.h

 // Copyright 2014 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_PPC_CONSTANTS_PPC_H_
 #define V8_PPC_CONSTANTS_PPC_H_
 
 #include <stdint.h>
 
 #include "src/base/logging.h"
@@ skipping 574 matching lines @@
  public:
   // Return the name of the register.
   static const char* Name(int reg);
 
   // Lookup the register number for the name provided.
   static int Number(const char* name);
 
  private:
   static const char* names_[kNumFPRegisters];
 };
-}
-}  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_PPC_CONSTANTS_PPC_H_