[presubmit] Enable readability/namespace linter checking.

src/extensions/free-buffer-extension.h

 // Copyright 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.
 
 #ifndef V8_EXTENSIONS_FREE_BUFFER_EXTENSION_H_
 #define V8_EXTENSIONS_FREE_BUFFER_EXTENSION_H_
 
 #include "include/v8.h"
 
 namespace v8 {
 namespace internal {
 
 class FreeBufferExtension : public v8::Extension {
  public:
   FreeBufferExtension()
       : v8::Extension("v8/free-buffer", "native function freeBuffer();") {}
   virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
       v8::Isolate* isolate, v8::Local<v8::String> name);
   static void FreeBuffer(const v8::FunctionCallbackInfo<v8::Value>& args);
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_EXTENSIONS_FREE_BUFFER_EXTENSION_H_