Remove the checksum/HMAC code from the decryptor.

media/mp4/track_run_iterator.cc

 // Copyright (c) 2012 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/mp4/track_run_iterator.h"
 
 #include <algorithm>
 
 #include "media/base/stream_parser_buffer.h"
 #include "media/mp4/rcheck.h"
@@ skipping 421 matching lines @@
        static_cast<size_t>(sample_size()))) {
     DVLOG(1) << "Incorrect CENC subsample size.";
     return scoped_ptr<DecryptConfig>();
   }
 
   const std::vector<uint8>& kid = track_encryption().default_kid;
   return scoped_ptr<DecryptConfig>(new DecryptConfig(
       std::string(reinterpret_cast<const char*>(&kid[0]), kid.size()),
       std::string(reinterpret_cast<const char*>(cenc_info.iv),
                   arraysize(cenc_info.iv)),
-      std::string(),  // No checksum in MP4 using CENC.
       0,  // No offset to start of media data in MP4 using CENC.
       cenc_info.subsamples));
 }
 
 }  // namespace mp4
 }  // namespace media