Add support for encrypted WebM files as defined in the RFC.

media/crypto/decryptor.h

Index: media/crypto/decryptor.h
diff --git a/media/crypto/decryptor.h b/media/crypto/decryptor.h
new file mode 100755
index 0000000000000000000000000000000000000000..de92421bb60f9e86617df795e57fddfd70da278c
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+++ b/media/crypto/decryptor.h
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+// 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.
+
+#ifndef MEDIA_BASE_DECRYPTOR_H_
+#define MEDIA_BASE_DECRYPTOR_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "media/base/media_export.h"
+
+namespace crypto {
+class SymmetricKey;
+}
+
+namespace media {
+
+class DecoderBuffer;
+
+// Interface for decrypting frames.
+class MEDIA_EXPORT Decryptor {
+ public:
+  Decryptor();
+  virtual ~Decryptor();
+
+  // Add a |key_id| and |key| pair to the key system. The key is not limited to
+  // a decryption key. It can be any data that the key system accepts, such as
+  // a license. If multiple calls of this function set different keys for the
+  // same |key_id|, the older key will be replaced by the newer key.
+  virtual void AddKey(const uint8* key_id, int key_id_size,
+                      const uint8* key, int key_size) = 0;
+
+  // Decrypt |input| buffer. The |input| should not be NULL.
+  // Return a DecoderBuffer with the decrypted data if decryption succeeded.
+  // Return NULL if decryption failed.
+  virtual scoped_refptr<DecoderBuffer> Decrypt(
+      const scoped_refptr<DecoderBuffer>& input) = 0;
+
+  // Decrypt |input| using |key|. |offset| is the number of bytes into |input|
+  // the encrypted data is.
+  // Return a DecoderBuffer with the decrypted data if decryption succeeded.
+  // Return NULL if decryption failed.
+  static scoped_refptr<DecoderBuffer> DecryptData(const DecoderBuffer& input,
+                                                  crypto::SymmetricKey* key,
+                                                  int offset);
+
+  // Generates a 16 byte CTR counter block. The format is
+  // | iv | block counter |. |iv| is an 8 byte CTR IV. Returns counter block on
+  // success. Returns empth string on failure.
+  static std::string GenerateCounterBlock(uint64 iv);
+
+ protected:
+  base::Lock lock_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(Decryptor);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_DECRYPTOR_H_