[presubmit] Enable readability/namespace linter checking.

src/extensions/externalize-string-extension.h

 // Copyright 2010 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_EXTERNALIZE_STRING_EXTENSION_H_
 #define V8_EXTENSIONS_EXTERNALIZE_STRING_EXTENSION_H_
 
 #include "include/v8.h"
 
 namespace v8 {
 namespace internal {
 
 class ExternalizeStringExtension : public v8::Extension {
  public:
   ExternalizeStringExtension() : v8::Extension("v8/externalize", kSource) {}
   virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
       v8::Isolate* isolate, v8::Local<v8::String> name);
   static void Externalize(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void IsOneByte(const v8::FunctionCallbackInfo<v8::Value>& args);
 
  private:
   static const char* const kSource;
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_EXTENSIONS_EXTERNALIZE_STRING_EXTENSION_H_