media config: expand is_encrypted to a struct.

media/base/media_util.cc

 // Copyright 2015 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/base/media_util.h"
 
 namespace media {
 
 std::vector<uint8_t> EmptyExtraData() {
   return std::vector<uint8_t>();
 }
 
+EncryptionScheme Unencrypted() {
+  return EncryptionScheme(EncryptionScheme::kCipherModeUnencrypted);
+}
+
+EncryptionScheme AesCtrEncryptionScheme() {
+  return EncryptionScheme(EncryptionScheme::kCipherModeAesCtr);
+}
+
 }  // namespace media