Implement "Key Presence" step in "Encrypted Block Encounted" algorithm in EME.

media/base/decryptor.h

 // 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/callback.h"
 #include "base/memory/ref_counted.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 class DecoderBuffer;
 
 // Performs key operations and decrypts encrypted buffer.
 // All public methods other than Decrypt() will be called on the renderer
 // thread. Therefore, these calls should be fast and nonblocking, with key
 // events fired asynchronously. Decrypt() will be called on the (video/audio)
-// decoder thread synchronously.
+// decoder thread.
 class MEDIA_EXPORT Decryptor {
  public:
   enum KeyError {
     kUnknownError = 1,
     kClientError,
     kServiceError,
     kOutputError,
     kHardwareChangeError,
     kDomainError
   };
@@ skipping 37 matching lines @@
   // decrypted and the decrypted buffer is ready to be read.
   // If the returned status is kNoKey, no decryption key is available to decrypt
   // |encrypted| buffer. In this case the decrypted buffer must be NULL.
   // If the returned status is kError, unexpected error has occurred. In this
   // case the decrypted buffer must be NULL.
   typedef base::Callback<void(DecryptStatus,
                               const scoped_refptr<DecoderBuffer>&)> DecryptCB;
   virtual void Decrypt(const scoped_refptr<DecoderBuffer>& encrypted,
                        const DecryptCB& decrypt_cb) = 0;
 
+  // Stops the decryptor and fires any pending DecryptCB immediately.

[scherkus (not reviewing), 2012/08/02 18:05:32]

fires the cb with what result?

[xhwang, 2012/08/03 20:08:10]

Done.

+  virtual void Stop() = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Decryptor);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DECRYPTOR_H_