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

media/crypto/aes_decryptor.cc

 // 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.
 
 #include "media/crypto/aes_decryptor.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/string_number_conversions.h"
 #include "crypto/encryptor.h"
@@ skipping 263 matching lines @@
 
   DecryptionKey* key = NULL;
   {
     base::AutoLock auto_lock(key_map_lock_);
     KeyMap::const_iterator found = key_map_.find(key_id);
     if (found != key_map_.end())
       key = found->second;
   }
 
   if (!key) {
-    // TODO(fgalligan): Fire a need_key event here and add a test.
     DVLOG(1) << "Could not find a matching key for given key ID.";
-    decrypt_cb.Run(kError, NULL);
+    decrypt_cb.Run(kNoKey, NULL);
     return;
   }
 
   int checksum_size = encrypted->GetDecryptConfig()->checksum().size();
   // According to the WebM encrypted specification, it is an open question
   // what should happen when a frame fails the integrity check.
   // http://wiki.webmproject.org/encryption/webm-encryption-rfc
   if (checksum_size > 0 &&
       !key->hmac_key().empty() &&
       !CheckData(*encrypted, key->hmac_key())) {
@@ skipping 49 matching lines @@
 
   hmac_key_ = DeriveKey(secret_, kWebmHmacSeed, kWebmSha1DigestSize);
   if (hmac_key_.empty()) {
     return false;
   }
 
   return true;
 }
 
 }  // namespace media