Use std::string for decryption key ID in webm parser.

media/webm/webm_content_encodings_client.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/webm/webm_content_encodings_client.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "media/webm/webm_constants.h"
 
@@ skipping 230 matching lines @@
 }
 
 // Multiple occurrence restriction is checked in this function.  Mandatory
 // restriction is checked in OnListEnd.
 bool WebMContentEncodingsClient::OnBinary(int id, const uint8* data, int size) {
   DCHECK(cur_content_encoding_.get());
   DCHECK(data);
   DCHECK_GT(size, 0);
 
   if (id == kWebMIdContentEncKeyID) {
-    if (cur_content_encoding_->encryption_key_id() ||
-        cur_content_encoding_->encryption_key_id_size()) {
+    if (!cur_content_encoding_->encryption_key_id().empty()) {
       DVLOG(1) << "Unexpected multiple ContentEncKeyID";
       return false;
     }
     cur_content_encoding_->SetEncryptionKeyId(data, size);
     return true;
   }
 
   // This should not happen if WebMListParser is working properly.
   DCHECK(false);
   return false;
 }
 
 }  // namespace media