Replace WIDEVINE_CDM_AVAILABLE with a gyp define 'enable_widevine_cdm'.

chromecast/media/base/key_systems_common.cc

Index: chromecast/media/base/key_systems_common.cc
diff --git a/chromecast/media/base/key_systems_common.cc b/chromecast/media/base/key_systems_common.cc
index 568aaa8a3e1e6e7d2fda92cd73e26d0d02624278..79f07a041f4ac90468a6d2fcc4789838f8517cc7 100644
--- a/chromecast/media/base/key_systems_common.cc
+++ b/chromecast/media/base/key_systems_common.cc
@@ -18,11 +18,11 @@ const char kChromecastPlayreadyKeySystem[] = "com.chromecast.playready";
 #endif  // defined(PLAYREADY_CDM_AVAILABLE)
 
 CastKeySystem GetKeySystemByName(const std::string& key_system_name) {
-#if defined(WIDEVINE_CDM_AVAILABLE)
+#if defined(ENABLE_WIDEVINE_CDM)
   if (key_system_name.compare(kWidevineKeySystem) == 0) {
     return KEY_SYSTEM_WIDEVINE;
   }
-#endif  // defined(WIDEVINE_CDM_AVAILABLE)
+#endif  // defined(ENABLE_WIDEVINE_CDM)
 
 #if defined(PLAYREADY_CDM_AVAILABLE)
   if (key_system_name.compare(kChromecastPlayreadyKeySystem) == 0) {