Remove the checksum/HMAC code from the decryptor.

media/mp4/track_run_iterator.cc

Index: media/mp4/track_run_iterator.cc
diff --git a/media/mp4/track_run_iterator.cc b/media/mp4/track_run_iterator.cc
index 073eeeecbde941ee35c2b11fcf6754926e8f0da2..36ec206d66236271993ee2e9ca202b3c455d4ff0 100644
--- a/media/mp4/track_run_iterator.cc
+++ b/media/mp4/track_run_iterator.cc
@@ -439,7 +439,6 @@ scoped_ptr<DecryptConfig> TrackRunIterator::GetDecryptConfig() {
       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));
 }