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.h

@@ -84,6 +84,9 @@ extern const char kSharedWorker[];
 extern const char kPageVisibility[];
 extern const char kOpenerID[];
 
+extern const char kWidevineCdmPath[];
+extern const char kWidevineCdmVersion[];
+
 }  // namespace switches
 
 }  // namespace atom