Move ENABLE_PEPPER_CDMS to a buildflag header.

media/base/key_systems.h

Index: media/base/key_systems.h
diff --git a/media/base/key_systems.h b/media/base/key_systems.h
index 0471e63351d414728eddf657e8de4015bd89759a..b6d9cee2aa16eb550aec3857b43a13337cd82022 100644
--- a/media/base/key_systems.h
+++ b/media/base/key_systems.h
@@ -12,6 +12,7 @@
 
 #include "media/base/eme_constants.h"
 #include "media/base/media_export.h"
+#include "ppapi/features/features.h"
 
 namespace media {
 
@@ -82,7 +83,7 @@ MEDIA_EXPORT std::string GetKeySystemNameForUMA(const std::string& key_system);
 // Returns whether AesDecryptor can be used for the given |key_system|.
 MEDIA_EXPORT bool CanUseAesDecryptor(const std::string& key_system);
 
-#if defined(ENABLE_PEPPER_CDMS)
+#if BUILDFLAG(ENABLE_PEPPER_CDMS)
 // Returns the Pepper MIME type for |key_system|.
 // Returns empty string if |key_system| is unknown or not Pepper-based.
 MEDIA_EXPORT std::string GetPepperType(const std::string& key_system);