Add ProxyDecryptor which wraps concrete Decryptor implementations.

webkit/media/crypto/key_systems.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 WEBKIT_MEDIA_KEY_SYSTEMS_H_
-#define WEBKIT_MEDIA_KEY_SYSTEMS_H_
+#ifndef WEBKIT_MEDIA_CRYPTO_KEY_SYSTEMS_H_
+#define WEBKIT_MEDIA_CRYPTO_KEY_SYSTEMS_H_
 
 #include <string>
 #include <vector>
 
+#include "base/memory/scoped_ptr.h"
+
 namespace WebKit {
 class WebString;
 }
 
+namespace media {
+class Decryptor;
+class DecryptorClient;
+}
+
 namespace webkit_media {
 
 // Returns whether |key_sytem| is supported at all.
 // Call IsSupportedKeySystemWithMediaMimeType() to determine whether a
 // |key_system| supports a specific type of media.
 bool IsSupportedKeySystem(const WebKit::WebString& key_system);
 
 // Returns whether |key_sytem| supports the specified media type and codec(s).
 bool IsSupportedKeySystemWithMediaMimeType(
     const std::string& mime_type,
     const std::vector<std::string>& codecs,
     const std::string& key_system);
 
+// Creates and returns a decryptor that corresponds to the |key_system|.
+// Returns NULL if the |key_system| is not supported.
+scoped_ptr<media::Decryptor> CreateDecryptor(const std::string& key_system,
+                                             media::DecryptorClient* client);
+
 }  // namespace webkit_media
 
-#endif  // WEBKIT_MEDIA_KEY_SYSTEMS_H_
+#endif  // WEBKIT_MEDIA_CRYPTO_KEY_SYSTEMS_H_