EME: Remove the concept of a parent key system.

media/cdm/key_system_names.h

 // Copyright 2013 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_CDM_KEY_SYSTEM_NAMES_H_
 #define MEDIA_CDM_KEY_SYSTEM_NAMES_H_
 
 #include <string>
 
 #include "media/base/media_export.h"
 
 namespace media {
 
 // TODO(jrummell): Change other uses of Clear Key to use this common value.
 
 // The key system name for Clear Key.
 MEDIA_EXPORT extern const char kClearKey[];
 
 // The key system name for External Clear Key.
 MEDIA_EXPORT extern const char kExternalClearKey[];
 
 // Returns true if |key_system| is Clear Key, false otherwise.
 MEDIA_EXPORT bool IsClearKey(const std::string& key_system);
 
-// Returns true if |key_system| is (reverse) sub-domain of |parent_key_system|.
-MEDIA_EXPORT bool IsParentKeySystemOf(const std::string& parent_key_system,
-                                      const std::string& key_system);
+// Returns true if |key_system| is (reverse) sub-domain of |base|.
+MEDIA_EXPORT bool IsChildKeySystemOf(const std::string& key_system,
+                                     const std::string& base);
 
 // Returns true if |key_system| is External Clear Key, false otherwise.
 MEDIA_EXPORT bool IsExternalClearKey(const std::string& key_system);
 
 }  // namespace media
 
 #endif  // MEDIA_CDM_KEY_SYSTEM_NAMES_H_