Cleanup: Pass std::string as const reference from media/

media/cast/common/transport_encryption_handler.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 MEDIA_CAST_COMMON_TRANSPORT_ENCRYPTION_HANDLER_H_
 #define MEDIA_CAST_COMMON_TRANSPORT_ENCRYPTION_HANDLER_H_
 
 // Helper class to handle encryption for the Cast Transport library.
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_piece.h"
 #include "base/threading/non_thread_safe.h"
 
 namespace crypto {
 class Encryptor;
 class SymmetricKey;
 }
 
 namespace media {
 namespace cast {
 
 class TransportEncryptionHandler : public base::NonThreadSafe {
  public:
   TransportEncryptionHandler();
   ~TransportEncryptionHandler();
 
-  bool Initialize(std::string aes_key, std::string aes_iv_mask);
+  bool Initialize(const std::string& aes_key, const std::string& aes_iv_mask);
 
   bool Encrypt(uint32 frame_id,
                const base::StringPiece& data,
                std::string* encrypted_data);
 
   bool Decrypt(uint32 frame_id,
                const base::StringPiece& ciphertext,
                std::string* plaintext);
 
   bool is_activated() const { return is_activated_; }
 
  private:
   scoped_ptr<crypto::SymmetricKey> key_;
   scoped_ptr<crypto::Encryptor> encryptor_;
   std::string iv_mask_;
   bool is_activated_;
 
   DISALLOW_COPY_AND_ASSIGN(TransportEncryptionHandler);
 };
 
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_COMMON_TRANSPORT_ENCRYPTION_HANDLER_H_