Basically make DecryptCentBuffer polymorphic.
https://cs.chromium.org/chromium/src/media/cdm/cenc_decryptor.cc

Currently DecryptCencBuffer always uses crypto::Encryptor but it would be useful by other decryptors such as D3D11Decryptor.
https://cs.chromium.org/chromium/src/media/gpu/windows/d3d11_decryptor.h

Change it so that it takes an AES CTR decryptor so that the decryption implementation can be switched dynamically.