Create an interface for KeySystems, migrate WebEncryptedMediaClientImpl.

media/base/eme_constants.h

 // Copyright 2014 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_BASE_EME_CONSTANTS_H_
 #define MEDIA_BASE_EME_CONSTANTS_H_
 
 #include <stdint.h>
 
 namespace media {
@@ skipping 72 matching lines @@
   EME_FEATURE_OPTIONAL,
   EME_FEATURE_REQUIRED,
 };
 
 enum class EmeMediaType {
   AUDIO,
   VIDEO,
 };
 
 // Robustness values understood by KeySystems.
-// Note: KeySystems expects this ordering (in GetRobustnessConfigRule()),
-// changes may be required there if this list changes.
+// Note: key_systems.cc expects this ordering in GetRobustnessConfigRule(),
+// make sure to correct that code if this list changes.
 enum class EmeRobustness {
   INVALID,
   EMPTY,
   SW_SECURE_CRYPTO,
   SW_SECURE_DECODE,
   HW_SECURE_CRYPTO,
   HW_SECURE_DECODE,
   HW_SECURE_ALL,
 };
 
@@ skipping 15 matching lines @@
   // The configuration option is supported, but the user experience may be
   // improved if a distinctive identifier is available.
   IDENTIFIER_RECOMMENDED,
   // The configuration option is supported without conditions.
   SUPPORTED,
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_EME_CONSTANTS_H_