Add widevine third party

Add 2 new command options to use widevine:
- widevine-cdm-path: Path to widevine plugin
- widevine-cdm-version: Version of the widevine plugin

atom/common/options_switches.cc

@@ -148,6 +148,12 @@ const char kSharedWorker[]               = "shared-worker";
 const char kPageVisibility[]             = "page-visiblity";
 const char kOpenerID[]                   = "opener-id";
 
+// Widevine options
+// Path to Widevine CDM binaries.
+const char kWidevineCdmPath[] = "widevine-cdm-path";
+// Widevine CDM version.
+const char kWidevineCdmVersion[] = "widevine-cdm-version";
+
 }  // namespace switches
 
 }  // namespace atom