chromecast: Cleanup class/struct fwd declarations

chromecast/media/cma/pipeline/decrypt_util.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 CHROMECAST_MEDIA_CMA_PIPELINE_DECRYPT_UTIL_H_
 #define CHROMECAST_MEDIA_CMA_PIPELINE_DECRYPT_UTIL_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 
-namespace crypto {
-class SymmetricKey;
-}
-
 namespace chromecast {
 namespace media {
 
 class DecoderBufferBase;
 class DecryptContextImpl;
 
 using BufferDecryptedCB =
     base::Callback<void(scoped_refptr<DecoderBufferBase>, bool)>;
 
 // Create a new buffer which corresponds to the clear version of |buffer|.
 // Note: the memory area corresponding to the ES data of the new buffer
 // is the same as the ES data of |buffer| (for efficiency).
 // After the |buffer_decrypted_cb| is called, |buffer| is left in a inconsistent
 // state in the sense it has some decryption info but the ES data is now in
 // clear.
 void DecryptDecoderBuffer(scoped_refptr<DecoderBufferBase> buffer,
                           DecryptContextImpl* decrypt_ctxt,
                           const BufferDecryptedCB& buffer_decrypted_cb);
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_CMA_PIPELINE_DECRYPT_UTIL_H_