Clean-up coding style

extensions/common/features/api_feature.h

 // Copyright 2014 The Chromium 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 EXTENSIONS_COMMON_FEATURES_API_FEATURE_H_
 #define EXTENSIONS_COMMON_FEATURES_API_FEATURE_H_
 
+#include <string>
+
 #include "extensions/common/features/simple_feature.h"
 
 namespace extensions {
 
 class APIFeature : public SimpleFeature {
  public:
   APIFeature();
   virtual ~APIFeature();
 
   // extensions::Feature:
   virtual bool IsInternal() const OVERRIDE;
   virtual bool IsBlockedInServiceWorker() const OVERRIDE;
 
   virtual std::string Parse(const base::DictionaryValue* value) OVERRIDE;
 
  private:
   bool internal_;
   bool blocked_in_service_worker_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_FEATURES_API_FEATURE_H_