Replace WIDEVINE_CDM_AVAILABLE with a gyp define 'enable_widevine_cdm'.

third_party/widevine/cdm/widevine_cdm_common.h

Index: third_party/widevine/cdm/widevine_cdm_common.h
diff --git a/third_party/widevine/cdm/widevine_cdm_common.h b/third_party/widevine/cdm/widevine_cdm_common.h
index 9004555b8e54bf9c45b1e80eae2336e05b8e4032..e7a143da3d56c303721d4802ef0cf60ae8e84f88 100644
--- a/third_party/widevine/cdm/widevine_cdm_common.h
+++ b/third_party/widevine/cdm/widevine_cdm_common.h
@@ -5,6 +5,8 @@
 #ifndef WIDEVINE_CDM_WIDEVINE_CDM_COMMON_H_
 #define WIDEVINE_CDM_WIDEVINE_CDM_COMMON_H_
 
+#if defined(ENABLE_WIDEVINE_CDM)
+
 #include "base/files/file_path.h"
 
 // This file defines constants common to all Widevine CDM versions.
@@ -66,4 +68,6 @@ const char kCdmSupportedCodecAvc1[] = "avc1";
 #endif  // defined(OS_MACOSX) || defined(OS_WIN)
 #endif  // defined(ENABLE_PEPPER_CDMS)
 
+#endif  // defined(ENABLE_WIDEVINE_CDM)
+
 #endif  // WIDEVINE_CDM_WIDEVINE_CDM_COMMON_H_