[presubmit] Enable readability/namespace linter checking.

src/base/cpu.h

 // Copyright 2006-2013 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.
 
 // This module contains the architecture-specific code. This make the rest of
 // the code less dependent on differences between different processor
 // architecture.
 // The classes have the same definition for all architectures. The
 // implementation for a particular architecture is put in cpu_<arch>.cc.
 // The build system then uses the implementation for the target architecture.
@@ skipping 127 matching lines @@
   bool has_popcnt_;
   bool has_idiva_;
   bool has_neon_;
   bool has_thumb2_;
   bool has_vfp_;
   bool has_vfp3_;
   bool has_vfp3_d32_;
   bool is_fp64_mode_;
 };
 
-} }  // namespace v8::base
+}  // namespace base
+}  // namespace v8
 
 #endif  // V8_BASE_CPU_H_