Getting rid of duplicate includes from media/

media/cdm/key_system_names.cc

 // Copyright 2013 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.
 
 #include "media/cdm/key_system_names.h"
 
-#include <string>
 
 namespace media {
 
 const char kClearKey[] = "org.w3.clearkey";
 const char kExternalClearKey[] = "org.chromium.externalclearkey";
 
 bool IsClearKey(const std::string& key_system) {
   return key_system == kClearKey;
 }
 
 bool IsParentKeySystemOf(const std::string& parent_key_system,
                          const std::string& key_system) {
   std::string prefix = parent_key_system + '.';
   return key_system.substr(0, prefix.size()) == prefix;
 }
 
 bool IsExternalClearKey(const std::string& key_system) {
   return key_system == kExternalClearKey ||
          IsParentKeySystemOf(kExternalClearKey, key_system);
 }
 
 }  // namespace media